If cheap credit made countries powerful, Japan would be the most powerful country in world history. They've had access to among the cheapest rates of credit for two decades, a time in which their economic output has gone nowhere.

Cheap credit helps one party and harms another within a country. It doesn't make a nation powerful. Technology, invention, scientific output, universities, capital for investment, scale, production / manufacturing, attractiveness to foreign talent and investment, modestly sane regulatory and tax policies, strong protections for property rights, ease of establishing and doing business, ease of trade, etc. Those are a few of the things that help to make a nation powerful. Those are things the US has either been the leader in or one of the leaders for the last century plus.

Much of Western Europe has had cheaper borrowing than the US for many years now, including in real-estate, corporate borrowing and at the government level. It didn't spur a great boom and increase their power. At best it has helped them tread water, which is all it did for Japan.