(CNN) Four issues have dominated the Israeli-Palestinian conflict as the most difficult to solve and the most complex to handle: the status of Jerusalem, Palestinian refugees (and their right of return), borders, and settlements.

Recent announcements by the Israeli government of the expansion of West Bank settlements, made in the period since Donald Trump became US President, have put settlements back in the spotlight. The announcements come just weeks after the UN Security Council Resolution declared that settlements had "no legal validity."

What are settlements?

Settlements are Israeli cities, towns and villages in the West Bank and the Golan Heights. (We will deal with East Jerusalem a bit later.) They tend to be gated communities with armed guards at the entrances. Why are they settlements and not simply Israeli residential areas? Because Israel is widely considered to be an occupying force in the territories. It is land that Palestinians, along with the international community, view as territory for a future Palestinian state.

Why are the West Bank and East Jerusalem considered occupied territory?

Israel began its occupation of the West Bank and East Jerusalem in 1967 during the Six-Day War. Seeing a military buildup in the surrounding Arab countries, Israel launched a preemptive strike against Egypt, after which Jordan, in turn, attacked Israel. Israel annexed East Jerusalem shortly thereafter, unifying the city under Israel's authority. But Israel has never annexed the West Bank, part of which remains under military law.

Decisions in the West Bank are carried out by the Israeli military, not the civilian government. The Israeli military makes decisions on land use, freedom of movement of Palestinians, home demolitions, and many other areas.

Before 1967, the West Bank and East Jerusalem were under Jordanian occupation. Jordan annexed the territory in 1950, but few countries recognized the annexation as legal. Jordan renounced its claim to this territory in 1988, recognizing the Palestinian Liberation Organization (PLO) as the representative of the Palestinian people.

Israelis who support the settlement movement, among a few others, dispute that the West Bank is occupied territory. They refer to the West Bank as Judea and Samaria, which is its biblical name. There are others who support this belief, including evangelical Christians. This opinion opposes the international consensus that the West Bank is occupied territory.

Where are the settlements?

There are 126 Israeli settlements in the West Bank (excluding East Jerusalem), according to the September 2016 report from the Israeli Central Bureau of Statistics. Geographically, these settlements are all across the West Bank.

The West Bank is broken down into Areas A, B, and C, according to the Oslo Accords, a series of peace agreements made in the 1990s.

Area C makes up approximately 60% of the West Bank. This area is entirely under Israeli control. Most of the settlements are in Area C.

Area B is under joint control between Israel and the Palestinian Authority and comprises approximately 20% of the West Bank. Area A is under full control of the Palestinian Authority. This area makes up the final 20%.

Most settlers live in what are called the "settlement blocs." These are areas that have a high number of Jewish settlements. The three main blocs are Ariel in the north, Ma'ale Adumim near Jerusalem, and Gush Etzion in the southern West Bank. Other settlements are outside of these blocs.

Who are the settlers?

This is a very broad question, and requires a fair amount of generalization.

According to the YESHA Council, which is the organization that represents West Bank settlements, there are approximately 420,000 settlers in the West Bank.

Each of these people has their own reasons for choosing to live in the West Bank, but we can break them down into four broad categories:

1. Religious-National Settlers: The religious-national settlers tend to live in the West Bank for ideological reasons. The West Bank has thousands of years of Jewish history and many Jewish holy sites, and religious-national settlers believe these have always been the Land of Israel, as promised to the Jewish people in the Old Testament.

In the Book of Exodus in the Torah, as in the Old Testament, verse 23:31 states "I will establish your borders from the Red Sea to the Mediterranean Sea, and from the desert to the Euphrates River. I will give into your hands the people who live in the land, and you will drive them out before you."

According to scripture, some of these holy sites include: the Cave of the Patriarchs in Hebron, where Abraham, Isaac, and Jacob are buried; Shiloh, where the Ark of the Covenant rested before it was carried into Jerusalem; and the Tomb of Joseph in Nablus.

An Israeli settler holds a flag with slogans at the Amona outpost, northeast of Ramallah, on February 1, 2017.

2. Ultra-Orthodox Settlers: The Ultra-Orthodox tend to live in their own settlements. Modi'in Illit in the northern West Bank and Beitar Illiat in the southern West Bank are examples of Ultra-Orthodox settlements, also known as Haredi settlements. These are also two of the most populated settlements. Ultra-Orthodox settlements are generally located close to the Green Line, which is the 1949 Armistice Line that separates Israel from the West Bank. They generally don't live in the settlements for ideological reasons; rather, they choose to live in the settlements because housing there tends to be more affordable.

3. Economic Settlers: It's not only the Ultra-Orthodox who live in the settlements for economic reasons. Some secular settlers, among others, live in settlements near the Green Line and in the blocs because of more affordable housing or quality of life considerations. For example, the settlement of Ariel in the northern West Bank has a mostly secular population that has easy access to nearby highways leading into Israel's economic heartland.

4. Jordan Valley Settlers: In the decade after the 1967 Six-Day War, a group of settlements were established along the Jordan River; people who settled there saw themselves as a first line of defense. (A peace treaty with Jordan wasn't signed until 1994.) These settlements run north-south along the Jordan Valley in the West Bank. Many are agricultural towns, taking advantage of the fertile land near the Jordan River.

Again, these are broad generalizations, but without getting into a detailed analysis of the settlers, this is a good place to start.

What's the difference between settlements and outposts?

Settlements are authorized by the Israeli government. Some were retroactively authorized, meaning they were initially built illegally but later recognized by the Israeli military. By contrast, outposts are illegally built Israeli villages which have not been recognized or authorized by the Israeli government. In the past, Israel's High Court has ordered some outposts evacuated and razed, including Amona and Migron. According to Peace Now, a left-wing organization that tracks settlement growth, there are 97 Israeli outposts in the West Bank.

Why are the settlements controversial?

The settlements are built on land the Palestinians and the international community, along with some in the Israeli community, see as a future Palestinian state. Some of the settlements -- especially the blocs -- may be a part of Israel in a two-state solution through land swaps between Israelis and Palestinians. One concern, expressed by the European Union, and in the past by the US State Department, is that settlement expansion may make a contiguous, whole Palestinian state in the West Bank impossible.

For example, a string of east-west settlements in the northern West Bank threatens to cut the West Bank apart into northern and southern segments, split by Israeli settlements. This string of settlements includes Oranit, Etz Efraim, Kiryat Netafim, Ariel, Eli, Shiloh, Ma'ale Efraim, and others. Ma'ale Efraim is deep within the West Bank, much closer to Jordan than it is to Israel.

If one contiguous Palestinian state cannot be recognized, then the two-state solution may be dead.

Palestinians have long claimed that the expansion of settlements is a way for Israel to de facto seize the land, and that Israel is creating "facts on the ground" that will be very difficult to undo. For this reason, Palestinians demand a freeze to settlement construction before they are willing to resume negotiations.

The Israeli government's position, under Prime Minister Benjamin Netanyahu, is that settlements are not an obstacle to peace and that settlement expansion is a function of natural growth within existing settlements. Netanyahu has repeatedly said that the refusal of the Palestinians to accept Israel as a Jewish state within any borders is the primary obstacle to peace.

What does President Donald Trump think of the settlements?

President Trump's administration warned on February 2 that new Israeli settlement activity could potentially hamper the peace process, a new stance for a White House that has remained adamant in its support for Netanyahu.

Despite the shift in language, the White House said it hadn't taken an official position on Israeli settlements, saying it would wait until Trump meets with Netanyahu later in February to formally develop a position.

To date, the US State Department under Trump has made no comment following recent announcements by Israel of new settlement housing. Under previous administrations, the State Department would routinely issue sharp criticism of any plans to expand settlements, and demand a freeze on construction.

What is the legal status of settlements?

The settlements are illegal under international law. The Fourth Geneva Convention, which concerns civilian populations during a time of war, states in Article 49 that, "The Occupying Power shall not deport or transfer parts of its own civilian population into the territory it occupies."

United Nations Security Council resolution 2334, which the United States did not veto, and was passed in December 2016, angering Israel, reaffirms this position. It states that settlements have "no legal validity" and constitute "a flagrant violation under international law." The resolution references previous Security Council resolutions 242, 338, 446, 452, 465, 476, 478, 1397, 1515, and 1850. Of these, 465, 476, and 478 established that settlements have "no legal validity" in 1980.

The International Criminal Court (ICC) currently has a preliminary examination underway that is looking into Israeli actions, including settlements, in the occupied territories since Jun 13, 2014. The examination, which is meant to determine whether there is enough evidence to begin an official investigation, was launched on January 16, 2015.

Israel, along with a few legal analysts, disputes that settlements are illegal. There are three primary reasons they use. Some cite religious reasons, claiming religious scripture gives Jews a right to build anywhere in Israel and the West Bank. Others use historical reasons, saying Jews have lived in the region for thousands of years, and it remains their land.

Some others use legal reasons. In 2012, the Israeli government, under the direction of Prime Minister Netanyahu, published the Levy Commission Report, which summarized this legal position. The report rejected the applicability of the Fourth Geneva Convention to the West Bank, arguing that the West Bank was never a legitimate part of any Arab state. "Consequently, those conventions dealing with the administration of occupied territory and an occupied populations [sic] are not applicable to Israel's presence in Judea and Samaria," the report read.

This is not a position that any country or international forum has accepted.

What about East Jerusalem? And what is East Jerusalem anyway?

From 1948 to 1967, Jerusalem was divided by the Green Line, which is the cease-fire line of 1948 between Israel and Jordan. Although the city is now under Israeli governance, the distinction remains.

Under international law, settlements in East Jerusalem are no different than settlements in the West Bank. So why consider them separately?

Because Jerusalem has always held a special place in the Israeli-Palestinian conflict. Secretary Kerry singled out Jerusalem as one of the most sensitive and complex points, as did President Bill Clinton when he offered his ideas for peace in 2000. Both Israelis and Palestinians claim Jerusalem as the capital of their state.

Unlike the West Bank, Israel annexed East Jerusalem. In late-June of 1967, Israel expanded the municipal boundaries of Jerusalem to include East Jerusalem, applying Israeli law to the entire city and declaring a unified Jerusalem as the capital of Israel. No country has ever recognized this annexation, and there are currently no embassies in Jerusalem. There are approximately 200,000 Israelis, which the international community considers to be settlers, and 300,000 Palestinians in East Jerusalem.

Although the international community considers Jewish neighborhoods in East Jerusalem as settlements, Israel disputes this. To Israel, this is simply building in Israel's capital, despite international objections.

Under the partition plan of 1947, Jerusalem was supposed to be an international city open for all religions. The entire vision of the partition plan never came to fruition. Jerusalem was even supposed to have its own international airport. There is an abandoned airfield in northern Jerusalem, established in 1920 under the British Mandate, that was intended as the city's link to the world.

What about the Golan Heights?

The Golan Heights is also considered occupied territory, taken from Syria in the Six-Day War in 1967 as well. But the West Bank has become the focal point of the Arab-Israeli conflict. The Golan has, to a large extent, fallen off the agenda.

Unlike the West Bank, Israel has applied Israeli law to the Golan, effectively annexing it. The international community does not recognize this annexation.

Israel has held onto the Golan Heights because of its strategic importance. The elevated terrain allows whoever controls it to see into both northern Israel and southern Syria. At 9,232 feet, Mt. Hermon is the highest mountain in the area. The Golan Heights has a small population of Israeli settlers, along with Druze, many of whom remain loyal to Syria.

Has Israel ever withdrawn from settlements?

Yes, Israel has withdrawn from settlements on a few different occasions. In 1982, Israel began withdrawing from settlements in Sinai as part of the 1979 peace deal with Egypt. In 1989, the withdrawal was completed, constituting a full Israeli withdrawal from Sinai.

In 2005, Israel unilaterally withdrew from settlements in Gaza. At the same time, Israel also withdrew from some settlements in the northern West Bank.