Here's a rundown on the island and its significance.
The escalating threats between the USA and North Korea have thrown the tiny US territory of Guam into the headlines. Before Trump's tweets on the nuclear arsenal, Tillerson arrived in Guam on a previously scheduled visit after telling reporters he did not believe there was an imminent threat from North Korea and "Americans should sleep well at night".
Its proximity to China, Japan, the Philippines and the Korean Peninsula has long made the island an essential position for the us military.
Pyongyang said it was "carefully examining" a plan to strike Guam, which is home to about 163,000 people and a United States military base that includes a submarine squadron, an airbase and a Coast Guard group.
The U.S. keeps a Naval base and Coast Guard station in the south, and an Air Force base in the north that saw heavy use during the Vietnam War.
North Korea is not yet capable of delivering a nuclear payload to the U.S. ICBM missiles would have to enter space before falling on the continental U.S. and it appears as if North Korea has not advanced to the stage of creating a nuclear warhead that can withstand the extreme heat of leaving and re-entering the atmosphere, according to the New York Times Wednesday.
Yang Uk, a senior research fellow at the Korea Defense and Security Forum, said: "If North Korea really decides to fire missiles at Guam, they probably will not design the missile to actually reach the territory of Guam, but just arrange missiles to blow up before they land on Guam, just to threaten the U.S. or to show off their missile capability".
Guam is also home to around 167,742 people, and Guamanians are USA citizens by birth. THAAD, or the Terminal High Altitude Area Defense, is one of the U.S.'s main weapons against offensive missiles.
The naval base dates to 1898, when the USA took over Guam from Spain after the Spanish-American War.
Guam has limited self-government, with a popularly elected governor, small legislature and a non-voting delegate in the U.S. House of Representatives.
Two United States Air Force B-1B bombers, on August 7, conducted a 10-hour sequenced bilateral missions with South Korea and Japan showing that they are ready to "Fight Tonight".
Chief Cabinet Secretary Yoshihide Suga said at a press conference, "We can not tolerate such a clear provocative act to the security of the region and global society, including our country", urging Pyongyang to exercise restraint.
"There could be a power outage in North Korea that they mistake as a part of a pre-emptive attack".
"Some investors had wanted reasons to unwind their long positions built up in emerging market equities, and they found an opportunity in the latest bout of Korean tensions", said Kota Hirayama, senior emerging markets economist at SMBC Nikko Securities in Tokyo.