He will have an official visit with Italian Prime Minister Paolo Gentiloni when he heads to Rome.
The president thanked the troops and their families for their service to the country and vowed that the USA will "win" the fight against terrorism.
"I won't forget what you said", Trump told Pope Francis at the end of their roughly 30-minute private meeting Wednesday, in the Vatican, in Rome, the second stop of the presidential trip.
Besides reaching a decision on the climate agreement once back in Washington, Trump will also face a new crush of Russia-related controversies.
USA officials said he had enjoyed "robust" conversations with his allies in Sicily and had also learnt a lot - especially in the debate on climate change, which he has previously dismissed as a hoax. A novice in worldwide affairs, Trump has been surprisingly candid about the impact his conversations with world leaders have had in shaping his views on numerous issues. The last G-7 meeting in Ise-Shima, Japan in 2016 agreed to "fight all forms of protectionism", or the use of import taxes and regulations to favour domestic producers over imports.
Concluding two days at the G-7 Summit, Mr. Trump said his meetings on trade and security were fruitful. This time the G-7 leaders reiterated a "commitment to keep our markets open and to fight protectionism".
President Trump is introduced ahead of his speech to US military troops at Naval Air Station Sigonella, Saturday, in Sigonella, Italy. His Treasury secretary, Steven Mnuchin, says the United States reserves the right to be protectionist if trade arrangements are unfair to USA companies and workers.More news: G-7 leaders give US more time on climate deal
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Trump also said he leaves amid new hope among nations on "eradicating the terrorism that plagues humanity".
"He stands in stark isolation", said Alden Meyer, who has followed climate talks for two decades as director of policy at the Union of Concerned Scientists. Unlike numerous leaders, he does not plan a news conference, meaning he'll end his trip without a formal question-and-answer session with journalists that could have included queries about the investigation back home into contacts between Russian Federation and his election campaign.
If that holds, Trump will break with presidential precedent by not holding at least one lengthy question-and-answer session with the press while overseas. "Now it's time for Trump to make the right decision".
Trump, on the final leg of a nine-day tour of the Middle East and Europe, arrived in Sicily late Thursday after publicly criticizing partners in Brussels for what he called their "chronic underpayments" to the North Atlantic Treaty Organisation military alliance. He's been willing to risk disapproval, engaging in an extraordinary scolding of close allies over their responsibility to pay for mutual defense.
Leaders from Tunisia, Kenya, Ethiopia, Niger and Nigeria took part in the discussions in Sicilian town Taormina earlier on Saturday. The meeting with Merkel came just a day after Trump reportedly called Germans "bad". The president said recent terrorist attacks in Manchester, England and Egypt underscored the need for the U.S.to "defeat terrorism and protect civilization".
"I think we hit a home run no matter where we are", Trump told the soldiers.
The United States produces the most carbon emissions of any country apart from China.
Leaders of the G7 meet Friday and Saturday, including newcomers Emmanuel Macron of France and Theresa May of Britain in an effort to forge a new dynamic after a year of global political turmoil amid a rise in nationalism. "The leaders from Europe, Canada, and Japan have made it crystal clear that they intend to fully implement their national commitments under the Paris Agreement".