W. e. b. du bois argued that washington perpetuated what by not opposing white supremacy?

Oppression of blacks by whites

Booker T. Washington (1856-1915) believed in a patient process, not immediately challenging the views of white superiority.  He thought that by hard work and perseverance, over time the black community would prove itself equal to whites.

W.E.B. Du Bois (1868-1963) criticized Washington's views, believing that it was wrong to allow any continuance of the idea of white superiority over blacks.  He promoted social action and agitation to challenge such views, because as long as whites viewed blacks as unequal, they would never allow actual equality to occur, and oppression of blacks by whites would continue in various forms.

Because he proposed that all the treaties should be made through the league of nations.