It's a divide a conquer strategy, which they've successfully employed in neoliberal market economies to undermine the middle class, erode worker rights, lower birth rates and deconstruct families.

But mass-immigration has also been used for electoral gains (immigrants most likely end up voting for Labour) and intelligence efforts (playing host to dissidents to undermine foreign governments, cultivating assets, mapping terrorist groups, recruiting native speakers, e.g. the father of the akbar who blew himself up at the Ariana Grande concert was a Libyan Islamist exile who later joined an Al Qaeda affiliate.)