The EU-US diplomatic relationship is arguably the most important diplomatic relation in the Western sphere of influence. As the EU parliament liaison office in Washington phrases it:

Diplomatic relations between the EU and the U.S. date back to 1953. The relationship between the EU and the U.S. is one of the most important bilateral relationships in the world. The EU and U.S. are the biggest economic and military powers in the world, dominate global trade, play the leading roles in international political relations, and whatever one says matters a great deal, not only to the other, but to much of the rest of the world.

A strong diplomatic transatlantic relationship between the EU and the US has the potential to shape much of the global balance of power, as it has during the early 21st century. Similarly, a deteriorating of this relationship brings with it substantial geopolitical risks in North America, Europe, and the rest of the world.

One severe risk of a breakdown of transatlantic relations is the cutting of diplomatic ties. Diplomatic ties are typically cut in response to serious diplomatic transgressions or in cases of war, such as when the US severed diplomatic relations with Germany in 1917 or in the ongoing relationships with Iran and Syria.