Even though many find the US narcissistic, on the whole, it has been a global positive force. Take economics. The US is a leader in technology, finance, healthcare and aerospace. Its per-capita GDP is $94,000, 6x global average. Germany is at $65,000, China just below $15,000. The only nations outranking the US are financial hubs (like Switzerland, $1,26,000), tax-optimised jurisdictions (like Bermuda, $1,38,000), and resource-heavy economies with small populations (like Norway, $1,05,000). Britain's per-capita GDP of $55,000 is equivalent to that of Mississippi, the poorest state in the US.
During WW2, it was the US' manufacturing might - not just military strength - that tilted the outcome in favour of the Allies. Today, it's technology.