In about 195 AD, Septimius Severus, Rome's first African born Emperor pulled all the troops out of the the string of forts that guarded the frontier and sent them off to fight a war in Iraq against the Iranians. Illegal immigrants, Franks mostly at first, flooded across the borders. After the war with Iran attempts were made to expel them. This failed. The Roman elites were unwilling to spend the money or provide the sons to support the legions. Before 300 AD they had given the invaders land to settle on in Gaul and granted them amnesty - attracting more illegal immigrants...
Sound familiar?
Hmmm, I wonder what the Romney family would think about that.