Check this
https://en.wikipedia.org/wiki/List_of_countries_by_external_debtUnited states is number one, China is number ten, Russia is number twenty nine, and Germany is number eight. It means you're wrong if you think strong economy countries aren't in debt.
Debt isn't always bad for filthy rich people or countries, watch Robert Kiyosaki how he use debt to make more money and protect his wealth.
No country that has all it needs to survive which is why all the countries of the world from all continents go into economic relaions through their foreign policy. But despite this relations a nation's level of importance and respect around the world from other countries in the international scene is greatly influenced by how strong and powerful it's economy is. But that doesn't mean that been a strong economy make sit immune to debt as there's no country without debt it's servicing. Debt isn't bad as some of us may think.