Labor has traditionally been against mass immigration as it threatened their wages and also their way of life. They also had to deal with the consequences of living in close proximity to the immigrants.

This changed after WWII when traditional Marxism lost its allure and fostering immigration became a point of pride for the left who saw it as a means of demonstrating how progressive they were, while simultaneously destroying any sense of ethnic coherence in the countries they ruled.

The fact their values dovetailed with the tenants of new-liberal capitalism, in which the world is flattened and all cultural and regulatory barriers that threaten the free movement of capital and labor are removed, also helped.