What is preventing the United States from printing USD to buy up prized assets from foreign countries given that USD is the world's reserve currency? USD is accepted all over the world. U.S can easily print USD to buy up the most valuable assets from all over the world. Ethics aside. What is preventing the U.S from doing so? What did I miss out?
To a certain extent it can.  But not too much, else it will create a run on the dollar.  If speculators no longer trusted the dollar, they would sell it for other stores of value (like Euros, gold, etc...).  Foreign dollars would have to come home and be redeemed by real wealth which means less real wealth for the US domestic economy and inflation.  This can feed on itself and cause a self-reinforcing inflationary fire that would be difficult to put out.