President Donald Trump is fond of suggesting that the five branches of the U.S. armed forces are not enough. On Monday, he directed the Defense Department to create a Space Force as the sixth branch of the U.S. military, saying “We are going to have the Air Force and we are going to have the Space Force, separate but equal.” This follows a statement the president made in March while addressing the Miramar Marine Corps Air Station in California, in which he said, “Space is a war-fighting domain, just like the land, air and sea.”

This is a horrible proposition.

In making these statements, Trump is parroting lines from people who know a lot about war and nothing about space. First of all, space is considered a “province of mankind,” according to the Outer Space Treaty of 1967 - which the United States and more than 100 other countries are parties to. This treaty lays out the principle that space is a domain that belongs to us all, not just to some states.

Second, war in space is particularly dangerous because it is a uniquely pollutable domain. The more space pollution there is, the more difficult it is for any of us to use space.

Imagine that Montenegro went to war against Fiji and that the war extended into Trump’s new “war-fighting domain.” Even those two countries, if they would obtain relevant space capabilities, would be extremely dangerous, as a war in space would almost inevitably lead to the destruction of satellites and the creation of debris that would remain in orbit for decades.

Scale up and imagine a war in space between the United States and China. Such a conflict would be devastating, affecting not only the 1.7 billion citizens of China and the United States but all 7.6 billion inhabitants of Earth.

We often forget how dependent we are on the use of space. Space is not just for astronauts; it is not even primarily for astronauts. Space is for telecommunication, navigation, Earth observation satellites and so many other purposes that we take for granted. A day without the use of satellites would send modern society into disarray. Power grids would go down, transportation would become much more difficult, global banking would discontinue, and the Internet would fail.

The laws of war try to make sure that the consequences of a war are generally restricted to the countries fighting the war. A war in space could never achieve that. It would affect the global community and create significant damage to all. The United States would be the country to suffer the most because its dependence on space is by far the greatest, as it possesses the most satellites.

It is in the interest of the United States and the rest of the world to make sure that space never becomes a war-fighting domain. We can achieve that by continuing to make sure it is neither permissible nor opportune. The next logical step would be to agree that war in space is an international crime. China and Russia could be well-disposed toward establishing such an international norm; after all, they have proposed a treaty to ban the placement of weapons in space entirely - a proposal the United States has blocked for a decade.

Outer space is under threat, and it is high time for the international community to make sure that the threat does not become reality. If Trump wants to make his country more secure, he must join the cause.

Peter Wismer is an international legal consultant based in Denmark and Austria.