DEAL, England — For centuries they sailed to the south, conquistadors and colonists, wresting control of a continent’s riches and imposing alien ways of faith and governance.

Yet, in recent weeks, watching the inexorable exodus of migrants risking their lives to cross the Mediterranean toward Greece and Italy in leaky craft, it is tempting to wonder whether the tide has turned.

Now, it is the powers of Europe, which once divided Africa between them, that face an invasion that could reshape their societies.

The presence of outsiders seeking a niche in cosseted lands has long unsettled Europeans who boast of big-heartedness while protecting privileged lives built in part on oil, minerals and cheap labor from farther south.