A bit strange

Normally Americans are well-known for killing civilians, be it the Koreans, Vetinam, Iraq or Afghanistan… they have killed far more civilians then their actual enemies, i would not be wrong to say that Americans didn’t regret it and have actually invented a term for it… Collateral Damage… but if the country under-attack by USA retaliate by any mean or any person in that country announces to kill the invaders.. then this is considered a crime against Humanity…

why is this?