Military tensions between rival nations around the world have ratcheted up in recent weeks as Russia continues its saber-rattling, Iran threatens Israel with invasion, and North Korea fires missiles toward Japan.

Meanwhile, China has refused to back down in a confrontation with the Philippines over its man-made islands, and the U.S. has responded by deploying Navy ships to the area.

Russia and NATO troops continue to eye each other over the Ukrainian border, and this week, Putin ordered armored tanks to the border while a convoy of troop transports and heavy weapons have been spotted in occupied Crimea.

They sit opposite of four NATO battalions totaling some 4,000 troops assigned to protect Europe from Russian aggression deployed after Putin seized the Ukrainian’s Crimea peninsula in 2014.