The US, already well on its way up in the 20th Century, was spared during WW1 and WW2, while many other countries were devastated. It also had massive resource

The US, already well on its way up in the 20th Century, was spared during WW1 and WW2, while many other countries were devastated. It also had massive resources, nearly endless open land compared to Europe, oceans on two sides to guard it from any credible threats, and a lack of invaders or civil wars in the 20th Century. The US also used to be a lot more welcoming, and benefited from many talented immigrants, Einstein being perhaps the most well known.