Syrian President Bashar al-Assad, left, made a surprise visit to Moscow to thank Russian President Vladimir Putin for launching air-strikes against Islamist militants in Syria. It was reportedly his first visit outside Syria since 2011. #

Israel's Prime Minister Benjamin Netanyahu, left, shook hands with Palestine's President Mahmoud Abbas during a photo for the the World Climate Change Conference 2015 in France, on November 30, 2015. It was the first time the two men stood face-to-face in five years. #

Jeroen Dijsselbloem, left, head of euro zone, and Greek Finance Minister Yanis Varoufakis shook hands in Athens on January 30, 2015, after announcing that Greece's government would not cooperate with the EU and IMF. #

U.S. President Barack Obama greeted Pope Francis during an arrival ceremony at the White House in Washington September 23, 2015. The pontiff was on his first visit to the United States #

South Korean Foreign Minister Yun Byung-Se, right, shook hands with his Japanese counterpart Fumio Kishida, left, in Seoul on December 28, 2015. Japan apologized for its use of Korean “comfort women,” who were forced to work in Japanese brothels during World War II. #

Kenya's President Uhuru Kenyatta, left, shook hands with U.S. President Barack Obama, right, before a meeting at the State House in Nairobi on July 25, 2015. Obama’s trip to his father’s homeland was the first official visit by a sitting American head of state. #

U.S. Secretary of State John Kerry, seated, shook hands with Iranian Foreign Minister Javad Zarif in Vienna, Austria, on July 14, 2015. Iran and six major world powers reached a nuclear deal, capping more than a decade of negotiations. #

Pope Francis met with former Cuban President Fidel Castro in Havana, Cuba, on September 20, 2015. The pontiff was credited with helping ease the thaw between the Castro regime and the United States. #

Chinese President Xi Jinping, right, shook hands with Taiwan's President Ma Ying-jeou on November 7, 2015. #

U.S. President Barack Obama, right, and Cuban President Raul Castro shook hands at the start of their meeting at the United Nations General Assembly in New York September 29, 2015. The two countries formally reestablished diplomatic relations this year. #

India's Prime Minister Narendra Modi, right, shook hands with his Pakistani counterpart Nawaz Sharif in Lahore, Pakistan, on December 25, 2015. Modi’s visit to the Islamic nation was the first by an Indian prime minister since 2004. #