For example, if Person_1 from a country besides USA calls an American (Person_2), it makes it ok for the NSA to spy on everyone Person_2 calls (lets call them People_3), and everyone People_3 calls (People_4) and everyone People_4 calls... I assume they follow the same rules for internet traffic so they basically get all internet data even if they are technically not allowed to spy on Americans...
http://arstechnica.com/information-technology/2013/07/you-ma...