(CNN) Former national security adviser Michael Flynn pleaded guilty Friday to lying to the FBI about his contacts with the Russian ambassador during the presidential transition last year.

Court documents unsealed on Friday reveal that Flynn's guilty plea stems from a handful of false statements he made to FBI investigators when he was interviewed in late January 2017.

The lies were about a series of calls Flynn had with then-Russian Ambassador to the United States Sergey Kislyak. The calls were about two distinct events: a controversial vote at the United Nations and President Barack Obama's decision to punish Russia for meddling in the 2016 US election.

Here is a breakdown of the phone calls and subsequent lies that led to Flynn's guilty plea.

Discussing the UN vote on Israel

The Wall Street Journal reported in recent weeks that Special Counsel Robert Mueller's prosecutors were investigating the Trump transition team's activities surrounding the United Nations Security Council vote in late December 2016 to condemn Israeli settlements in Palestinian territories.

Before the vote, the Israeli government lobbied the Obama administration to kill the resolution, but its efforts fell flat. The Israeli government then reached out to Trump's team and asked him to help pressure the Obama administration to veto the resolution, a senior Israeli official told CNN at the time

"The resolution being considered at the United Nations Security Council regarding Israel should be vetoed," Trump said in a public Facebook post on the morning of December 22, 2016.

The resolution was originally proposed by Egypt. The same day he posted that message on Facebook, Trump spoke with Egyptian President Abdel Fattah al-Sisi before the scheduled vote. After the call, Egypt withdrew the proposal, but other countries later stepped in to put it back on the docket.

Later that same day Trump's incoming national security adviser, Flynn, asked then-Russian Ambassador Kislyak to "delay the vote on or defeat a pending United Nations Security Council resolution," according to the charging documents against Flynn that were unsealed on Friday.

The filings don't explicitly state that the UN resolution was about Israel. The documents also indicate that Kislyak then told Flynn about the Russian government's response to Flynn's request. Flynn pleaded guilty on Friday to a charge of lying to the FBI about what he had discussed with Kislyak on this call.

Ultimately, the US abstained from the vote, and the resolution passed 14-0 . The other members of the Security Council voted "yes," including Russia and US allies like the United Kingdom.

Shortly after the vote, Trump responded on Twitter : "As to the U.N., things will be different after Jan. 20th." One day after the vote, Trump condemned it on Twitter : "The big loss yesterday for Israel in the United Nations will make it much harder to negotiate peace. Too bad, but we will get it done anyway!"

In two tweets a few days after the vote, Trump continued to condemn the vote and criticize the Obama administration's position: "We cannot continue to let Israel be treated with such total disdain and disrespect. They used to have a great friend in the U.S., but....... not anymore. The beginning of the end was the horrible Iran deal, and now this (U.N.)! Stay strong Israel, January 20th is fast approaching!"

Discussing US sanctions against Russia

Days after the UN vote, the Obama administration announced new sanctions against Russia as punishment for the Kremlin's campaign to interfere in the 2016 election. The sanctions targeted Russia's intelligence services and Russian agencies that were involved in cyberactivities.

Flynn and Kislyak had phone conversations on December 29, 2016, the day that Obama announced the new sanctions and also expelled 35 Russian diplomats.

The charging document unsealed on Friday states that Flynn made a false statement to the FBI when he said that in December 2016 he did not ask Kislyak "to refrain from escalating the situation in response to sanctions that the United States had imposed against Russia that same day; and Flynn did not recall the Russian ambassador subsequently telling him that Russia had chosen to moderate its response to those sanctions as a result of his request."

One day after these phone calls, Russian President Vladimir Putin said he wouldn't retaliate against the United States and wouldn't impose new tit-for-tat sanctions -- puzzling officials in Washington.

Later that day, Trump praised this announcement on Twitter , throwing a compliment to the Russian leader: "Great move on delay (by V. Putin) - I always knew he was very smart!"

When Flynn's calls were first revealed earlier this year, White House officials insisted the conversations did not include sanctions — including denials that Vice President Mike Pence and former White House Chief of Staff Reince Priebus later repeated on national television.

Flynn resigned on February 13 after reports that he and Kislyak had spoken about sanctions and the Justice Department had warned the White House that Flynn was potentially vulnerable to blackmail by the Russians.