While the Trump administration has been focused on trade wars, China has found another way to challenge U.S. power — by using its signature overseas development policy, "The Belt and Road Initiative," to advance military interests, especially on the high seas.

China is using the debts it is owed by other countries to purchase or invest in strategically located ports around the world on terms favorable to Beijing. The country is investing in ports located near U.S. military bases in places like in Djibouti, countries like Israel and Greece, which are traditionally U.S. allies, and, increasingly, in Latin America.

"None of these issues are necessarily going to be a problem unless and until there's a conflict," said Carolyn Bartholomew, chairman of the U.S.-China Economic and Security Review Commission. "Then, there has to be concern about the Chinese shutting down U.S. access."

In the last few decades, China's Navy has gone from practically nonexistent to one of the largest navies in the world. Analysts see the "Belt and Road" initiative as key to extending Beijing's naval power, and realizing President Xi Jinping's goal of building a military capable of confronting the U.S. on the world stage.

Since 2013, China has lent or invested more than a $1 trillion abroad, much of it for port infrastructure, but that money often comes with significant strings attached. And when another country can't pay, China takes advantage.

"We found that six of the of the Belt and Road Initiative countries are countries that have benefited from debt relief the last time there was a major global debt relief package," Bartholomew said. "And another 26 or 27 of those countries are countries that essentially have a junk bond rating. So we have to be concerned about the ability of these countries to manage the debt that China is saddling them with."