Leverage Limitation for Retail Forex

Margin requirement fo US treasuy securities is 1% (at interactive brokers 6 month or less maturity)
100:1 because Bonds from the treasury are as good as cash.

Cash is as good as cash, isn't it?

Assuming 1/2 the small traders move offshore

This causes an outflow of US currency (to pounds or francs etc.) thus weakening the dollar

And half increase their account by 10X.
As for the enlarged accounts that money is now stagnant, not helping the economy at all. Not being spent, not being invested in production.

That's very possible. I sent my money to Germany and London respectively.

All that to say that they have accounts in many cities in the world. However, there must be one headquarter. The site lists both, New York City and Toronto.