The President-elect's decision to flout 40 years of diplomatic convention and take a call from Taiwanese President Tsai Ing-wen last week suggested he may be just as disrespectful of protocol on the world stage as at home.

The call produced days of speculation about how the President-elect's impulsive style will reverberate around the globe and whether it could threaten the architecture of international relations.

There are many global traditions and arrangements that he could target, though each could carry a geopolitical or diplomatic price -- one reason even presidents who have come into office with all guns blazing often find that there's a reason why some taboos last so long.

Here are some of the conventions Trump could shake up once he becomes president next month.

Talking to North Korea's Kim Jong Un

Even Obama, who was willing to engage historic US enemies like Iran and Cuba, has balked at speaking to North Korea's unpredictable leader, Kim Jong-un. The George W. Bush administration also snubbed Kim's equally volatile father and predecessor, the late Kim Jong Il. President Bill Clinton did mull a visit to North Korea late in his second term, but eventually decided not to go.

There have been direct contacts with Pyongyang through a channel at UN meetings between officials from the two sides in Beijing, and post-presidential missions to the Stalinist state by Clinton and Jimmy Carter.

But the idea of direct, presidential-level engagement with the leader of North Korea, who rules with an iron fist, has been taboo. One reason is that such talks would be seen as a reward for threats and behavior apparently designed to win concessions from Washington.

But with North Korea making swift advances in its nuclear and ballistic missile programs and threatening to precipitate the first international crisis of the Trump administration, could that change?

When asked by Reuters in May if he was ready to talk to Kim, Trump replied: "I would speak to him, I would have no problem speaking to him."

Again, it's easy to make such remarks on the campaign trail. A conversation would risk squandering presidential prestige unless it came with a high diplomatic deliverable, so Trump might balk. Still, given the President-elect's unpredictability and faith in his own skills as a deal-maker, it would be unwise to rule out contact with Kim just yet.

Moving the US Embassy in Israel to Jerusalem

Trump, like his predecessors Clinton and Bush, has voiced support for moving the US Embassy in Israel from Tel Aviv to Jerusalem. It's an easy vow for a candidate to make, especially since the issue is hugely important to the critical bloc of evangelical voters.

But it's one of those campaign vows that looks a lot less attractive viewed from the Oval Office.

The embassy is situated in Tel Aviv because the international community has not recognized Jerusalem as Israel's capital. Furthermore, the Palestinians also claim Jerusalem as the capital of their future state, so moving the US Embassy to Jerusalem would be extremely sensitive and seen by Arab states -- key to other US goals in the region -- as a sign that Washington is pre-judging final status peace talks between Israelis and Palestinians.

Though Congress has passed legislation mandating the move, these complications prompted Presidents Clinton, Bush and Barack Obama every six months to employ the law's waiver provision to put off the move on national security grounds.

But it's not clear that Trump will take the same stance.

"We will move the American Embassy to the eternal capital of the Jewish people, Jerusalem," Trump said at the annual meeting of the America Israel Public Affairs Committee in Washington in March.

Still, once he is embarked upon a presidency that will beset by global challenges, Trump may decide he doesn't want to ignite another crisis. So the White House will be under intense scrutiny once the next waiver is due, by June.

Human rights as a foreign policy priority

For successive administrations, the cause of human rights has been at the center of American foreign policy.

The issue does wax and wane in importance for different presidents. And there is often debate about whether a certain administration has de-emphasized human rights as a driver of relations with other countries. But human rights campaigners are especially worried about Trump.

He barely talked about the issue during his election campaign. And when he did, he provoked searching questions. In an interview with The New York Times in July, he declined to criticize Turkish President Recep Tayyip Erdogan for jailing thousands of political opponents and pointed out that the United States had its own share of problems.

"When the world looks at how bad the United States is, and then we go and talk about civil liberties, I don't think we're a very good messenger," Trump told the Times.

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Trump's admiration for the strongman leadership of Russian President Vladimir Putin, who is accused of severely curtailing civil liberties, also worries critics -- as do his warnings during the campaign that he would target the families of terror suspects in airstrikes, an apparent infringement of the Geneva Conventions.

The President-elect's recent telephone call with Philippine President Rodrigo Duterte was also an eye-opener. According to a readout from the government in Manila, Trump invited Duterte to the White House and seemed to convey understanding of his bloody extra-judicial war on drugs.

"It was, a bit, very encouraging in the sense that I supposed that what he really wanted to say was that we would be the last to interfere in the affairs of your own country," Duterte said.

The Trump transition has not offered its own details of the call. But Duterte's interpretation begs the question of whether Trump will skip over human rights issues as he seeks better relations with leaders like Duterte and Putin, who have been ostracized by the Obama administration.

Casting doubt on US alliances

For 70 years, US global power and the relative peace and security of the order that America built in the aftermath of World War II have been anchored on alliances. In Europe, NATO has often been referred to as the greatest defensive partnership in history and helped win the Cold War. In Asia, Washington's partnerships and security guarantees with Japan and South Korea kept the peace in a region now grappling with China's rise.

But if Trump makes good on some of his campaign rhetoric, those alliances could be in for radical reassessment.

The President-elect called on South Korea and Japan to pay the United States more for their protection by US troops.

He also appeared to cast doubt on the US-Japan security alliance.

"If somebody attacks Japan, we have to immediately go and start World War III, okay? If we get attacked, Japan doesn't have to help us. Somehow, that doesn't sound so fair," Trump said in South Carolina in January.

Such statements were one reason why Japanese Prime Minister Shinzo Abe hurried to New York last month to visit the President-elect.

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Trump's intentions towards NATO have also been questioned ever since he said Washington's willingness to defend its partners in the alliance would depend on whether they had met their financial and military obligations toward the organization.

He also said that NATO was "obsolete" and wasn't doing enough to fight terrorism.

Amid alarm in Europe, there are signs Trump has been backtracking in calls with allied leaders.

NATO Secretary General Jens Stoltenberg said Tuesday that he was "absolutely certain" the US would remain committed to the transatlantic alliance and security guarantees to Europe.

But the nervousness will persist until Trump visits Europe in person to deliver those sentiments publicly as president.

Dropping the careful talk about Islam

The two presidents in office since the September 11 attacks have been highly sensitive to any suggestions that the US war on terror was a war against Islam. Bush visited an Islamic cultural center in the days after 9/11 and Obama flew to Cairo in 2009 to offer "a new beginning" with the Muslim world. Just this week, Obama warned that stigmatizing "good, patriotic Muslims" feeds the narrative of terrorists.

But Trump is not known for careful language.

A year ago, he called for a "total and complete shutdown of Muslims entering the United States" after a radicalized couple launched an attack in San Bernardino, California.

The President-elect has since watered down the Muslim ban but is still planning to bar refugees from Syria and in the campaign mulled surveillance of mosques and databases for Muslims in the United States.

He has not renewed such calls since winning the election, but he has also not laid out a clear alternative policy either. And his elevation to national security adviser of retired Gen. Michael Flynn, who has a history of emotive rhetoric critical of Islam, has alarmed Obama administration officials and even some Republicans.

A more strident critique of Islam from the Oval Office would mark one of the most consequential breaks from the conventions followed by Trump's immediate predecessors.