The United States just grew by 1 million square kilometres in size

The United States might just be a whole lot bigger than you remember.

Just last month, the US expanded - by one million square kilometres to be exact - which is more than 386,000 square miles.

This unexpected expansion, nearly double the area of Spain, didn't result from geological factors nor was it any kind of nation invasion.

Instead, it's a strategic move by the United States to assert control and sovereignty over its surrounding extensive ocean-floor territories.

The US has expanded by one million square kilometres / NASA/Science Photo Library

Continental shelves are an area of submerged landmass that've become part of the seabed, in which the ocean depth is relatively shallow compared to the open ocean.

International laws permit nations to essentially claim these shelves as their Extended Continental Shelf (ECS), thereby gaining rights to manage and exploit their natural resources.

Globally, around 75 countries have marked their ECS limits, which extend beyond 200 nautical miles from their coasts.

Until recently, the US hadn't defined its ECS limits.

However, now the United States asserts ECS rights in seven offshore regions, including the Arctic, the east coast Atlantic, the Bering Sea, the west coast Pacific, the Mariana Islands, and two areas in the Gulf of Mexico.

Collectively, these areas expand across a huge one million square kilometres and, on December 19th, 2023, the US State Department defined the geographical coordinates as its ECS.

The US is unsure how the ECS will sit with international law / Getty Images/USGS Pacific Sea-Floor Mapping Project

Last month, Mead Treadwell, a former Alaska lieutenant governor and former chair of the U.S. Arctic Research Commission, said: 'America is larger than it was yesterday.'

'It’s not quite the Louisiana Purchase. It’s not quite the purchase of Alaska, but the new area of land and subsurface resources under the land controlled by the United States is two Californias larger,' he added.

To finalise these claims, the United States must present detailed data and reports to the United Nations Convention on the Law of the Sea (UNCLOS).

But the US hasn't agreed to an UNCLOS's sea law, even though 168 other countries and the European Union have. Due to this, it's not clear how the new territory will sit with international law.

Treadwell explained: 'If somebody came back and said, ‘Your science is bad, I think the United States would listen.'

'But I don’t think science is bad. I think we’ve had very good science.'

If the US does receive approval, it could open up future opportunities for mining, shipping and fishing trades - each with its own implications.