This is something that might make Bitcoin get to a million dollars as many people speculate. When a country like the US decides to have a bitcoin reserve other countries will certainly follow. Even if there wont be a buying war, the fact that other countries are trusting bitcoin enough to have a reserve will further increase the demand for bitcoin and this will make the price to sky rocket.

I don't think people should be scared that the countries will buy off all of the bitcoin. When bitcoin price become that high , countries wont be able to buy as much as they want to now. If the US want t buy 5 million bitcoin today, they wont be able to buy 5 million btc when the price of a bitcoin is $1 million.