The USA has been a prominent member of the North Atlantic Treaty Organisation (NATO) since it was established in 1949. NATO is the largest and most powerful military alliance in the world. As of 2022 it has 30 member states.
In theory, the organisation is made up of members of equal standing, where each country has one vote in decision-making.
In reality, the USA is the dominant player within NATO. It contributes far more troops, resources, and finances than any other single member of the alliance. As a result, it is the country most able to set the NATO agenda.
For example, it is claimed the USA has kept the pressure up on European countries to look to expand NATO eastwards.
In recent years, the USA has also tried to encourage the other members of NATO to take a greater responsibility for their own defence and to make a larger contribution to NATO's finances. It has been argued that the US has been focusing its attention more on Asia and the Far East as opposed to Europe.
However, after Russian annexation of the Crimea in 2014, NATO and American support for the Atlantic Alliance moved closer to the top of the US international agenda.
US leadership within NATO remains very important:
However, the US also needs NATO as it allows the US to confront difficult and diverse threats to its security alongside other countries which support democratic values. As part of NATO the US is stronger.
The 2022, the Russian invasion of Ukraine has become the biggest international issue for the USA.
Ukraine is not a member of Nato, so the alliance is not obliged to come to its defence. However, it is a "partner" country - there is an understanding it will join at some point in the future.
Some Nato nations have been sending weapons to Ukraine to help its defend itself against Russia. As of the end of February 2022, the US has sent $200m of weapons to Ukraine, and says it will send an extra $350m in weapons.
The US and many other nations have also worked to impose sanctions on President Putin, his associates and Russia.
The US and other NATO members face difficult decisions over how much to support Ukraine while not wishing for their armed forces to come into direct conflict with Russia.