In 2014, President Obama expanded the Pacific Remote Islands Marine National Monument, making it the largest marine preserve in the world at the time. The expansion closed 490,000 square miles of largely undisturbed ocean to commercial fishing and underwater mining.
The preserve is nowhere near the mainland United States nor is it all in close range to Hawaii. Still, President Obama was able to protect this piece of ocean in the name of the United States.
To understand how the U.S. has jurisdiction over these waters in the middle of the Pacific Ocean, one has to look back to the 19th Century when, for a brief period, the U.S. scoured the oceans looking for rock islands covered in guano. That is: seabird poop.