Why did some americans call david wilmot's proposal the "white man's proviso"?

The Wilmot Proviso" was also referred to as the "White Man's Proviso" because its sponsor, David Wilmot, was arguing for new territories to be dedicated to white settlement only. 

In 1846, Congressman David Wilmot of Pennsylvania introduced the proviso as an amendment to an appropriations bill in connection with the peace treaty being negotiated with Mexico.  His amendment stipulated that any territory gained from Mexico would be free, not allowing slavery.  Debated in 1847, Wilmot's amendment passed in the House of Representatives, but was unable to get approval in the Senate. Wilmot's reason for his proposal was not because he was defending the cause of blacks or seeking to outlaw slavery. In a speech he delivered in the House of Representatives in 1847, Wilmot said: "I make no war upon the South nor upon slavery in the South. I have no squeamish sensitiveness upon the subject of slavery, nor morbid sympathy for the slave. I plead the cause of the rights of white freemen. I would preserve for free white labor a fair country, a rich inheritance, where the sons of toil, of my own race and own color, can live without the disgrace which association with Negro slavery brings upon free labor."

this is a good question! i'll do some research and come back when i have the answer!

which statement explains one of the reasons world war 1 was so much more destructive than earlier conflicts