- Trans-Pacific Partnership -

Making good on a campaign pledge, Trump on his first full day in office withdrew from the 12-member trade pact negotiated by his predecessor.

He said the TPP -- which has yet to take effect but has been signed by participating nations -- left the United States exposed to unfair competition and was a bad deal.

But a year after taking office -- after the 11 other members signaled they would press ahead with or without Washington -- Trump struck a different tone, suggesting he would be open to joining again if the United States won unspecified changes.

- NAFTA -

After denouncing the 24-year-old North American Free Trade Agreement as a "disaster" and the "worst trade deal maybe ever," Trump last year called for the pact to be renegotiated, but stopped short of withdrawing.

Delegates from Mexico City, Ottawa and Washington are currently attempting to retool the deal, but they have hit serious stumbling blocks and the talks have been acrimonious in recent months.

Canada and Mexico oppose the American demand for higher requirements for US-made content in automobiles and the elimination of an important trade dispute mechanism.

The future of the agreement, which has seen sharp growth in trade but painful changes for certain industries, remains uncertain.

- Paris climate pact -

The US commitment to fighting climate change -- forged under former president Barack Obama -- was reversed in June 2017, when Trump announced he would withdraw America from the Paris pact.

As he announced his decision to pull out, Trump indicated he could be open to some sort of renegotiation of the voluntary agreement, but his administration has done nothing to follow up on this.

Meanwhile, more than 190 nations still in the pact are trying to how to cap global warming at "well under" two degrees Celsius (3.6 Fahrenheit).

- Jerusalem embassy -

Trump last year recognized Jerusalem as Israel's capital, a declaration condemned by the international community and Palestinians who view east Jerusalem as the capital of their future state.

In January, Washington announced it would transfer its embassy from Tel Aviv to Jerusalem in May to coincide with the 70th anniversary of the creation of Israel.

- North Korea -

After months of bellicose rhetoric between Trump and North Korean leader Kim Jong Un, the US president in March said the two would meet for a summit, a stunning development South Korea's President Moon Jae-in dubbed a "miracle."

The move came after Kim conducted repeated launches of intercontinental ballistic missiles and carried out a nuclear test.

North Korea freed three American detainees Wednesday, handing them over to Secretary of State Mike Pompeo who was on a surprise visit to Pyongyang.

Kim has already meet with Moon, and the summit with Trump is expected in the coming weeks.

- Syria -

Last month, Trump said he wants American troops to "get out" of Syria, but his top military officials quickly said there was no change to the US mission to beat the Islamic State group, and that US forces would remain for now.

Trump has twice ordered cruise missile strikes on the regime of President Bashar al-Assad after he was accused of using chemical weapons.

The most recent strike, in April, was conducted with the assistance of French and British forces.

- Iran deal -

Trump as a candidate and since taking office railed against the 2015 Iran deal, also known as the Joint Comprehensive Plan of Action (JCPOA).

The US president blasted the JCPOA as "insane" -- in part because its restrictions on Iran's nuclear activities begin expiring in 2025.

Despite a maximum diplomatic effort by European leaders including French President Emmanuel Macron and German Chancellor Angela Merkel, Trump on Tuesday did what many expected him to do, pulling America out and re-instating sanctions on Iran.