Currency

You know what, I don't know anything about the currency markets. What causes the dollar to fall against foreign currency? I had always assumed that it was due to an unfavorable balance of trade, but I'm not really sure any more. I don't think our trade balance has changed significantly in recent years, so I'm at a loss to explain the falling dollar. What am I missing? Are we borrowing a lot of money to finance the war? Are foreign investors, uh, doing something I don't know about? I can't begin to explain the shame of the US dollar being worth less than the Canadian dollar. And why aren't we being flooded with tourists? It should be very cheap for them to come here now. I'm at a loss. If someone can explain international finance to me, I'm all ears.