This is a question has been bothering me as someone who’s country was colonized by the British Empire. We were taught about it in schools and how it lost power over time but never how the USA came to take its place especially over such a short compared to the British Empire.
While everyone is talking about World War II, it is kind of important to discuss what led the USA to become capable of taking over.
First, the USA was a giant as a successor nation to American colonization. It had significant natural resources, a relatively easily navigable interior, and a budding industrial sector. Unlike Spanish colonies, the USA had pretty good national institutions where wealth could be created.
After the War of 1812, the UK had already shifted its strategic approach to the USA. The UK would allow the USA to be a local hegemon as long as the USA respected existing British colonial claims. This led to the Monroe Doctrine, partially enforced by the UK. There were also a lot of cases where the UK chose not to press claims to antagonize the USA. This included a peaceful solution to the Oregon Territory crisis and not participating in the French invasion of Mexico.
The USA was considered to be a rising great power by the end of the 19th century, including destroying the remnants of the Spanish Empire. Many nations recognized that the USA benefited from the same geographical features that the UK did, with the homeland being far removed from any other competing power.
The USA could have credibly become the leading great power after World War I had the USA not chosen to go into isolation after the war. By then, it was apparent that the USA had a military and economy to be a major international player, but the US Republican Party didn’t want to agree to the international commitments.
So, by the end of World War II, the USA was already the preminent economic power for at least a generation. The USA was then able to build a military capable of fighting a two front war while supplying many of its allies in the war. Meanwhile, the UK was seeing its empire fall apart and knew it couldn’t afford to be the international leader. Choosing between the USA and USSR, the UK chose the USA.