But they weren't founded on Christ's teachings. They used the Bible to justify maintaining their power -- divine right etc. -- but Europe's royal houses were founded on the acquistion of personal power.
And the United States is? Really? I assume you can direct me to some site on the internet where there's a copy of the US Constitution with footnotes indicating where each significant passage can be traced to something Jesus said. Hint: don't bother looking, it doesn't exist. You can sit down with your Bible and your Constitution beside it, and you cannot find (without wild squirming and re-interpretation) any scriptural basis for our form of government. Read the Federalist Papers. They do not justify the Constitution's provisions on scriptural grounds. Why not? Because the Bible is essentially about monarchies, both on earth and in heaven.