Why? To Jesus, his disciples, followers, and the unknown authors of the gospels who witnessed the destruction of Judea, the temple, their way of life, and the slaughter exile and enslavement of hundreds of thousands of Jewish men women and children "the nations" were the enemy. Duh.
"Take from my hand this cup of fiery wine and make all the nations to whom I send you drink it.
When they have drunk it they will vomit and go mad;
such is the sword that I am sending among them"
"From his mouth there went a sharp sword with which to
smite the nations."
"
He who lives by the sword shall die by the sword"