A Muslim man on US R1 (Religious Visa) was part of the group of terrorists responsible for 9/11. I think that's the worst immigration violence in the United States.

When Columbus landed in present day Haiti, he was sure that the "savages" had gold. He began enslaving them and ordering them to bring him gold each week. When they didn't bring gold, he cut their hands off as punishment.

The transatlantic slave trade was likely the worst instance of immigration violence in history. It involved the systematized brutality of men, women, and children and generations of their descendants. The widespread violence against the slaves was supported by immigration laws in hundreds of localities on both sides of the Atlantic.

The decision by the British to turn over Palestine to Jewish immgrants from Europe has caused almost a century of trouble and is still doing so.

Now, of course, if you were to ask the opinion of American Indians....

Ivorian civil war which was between the native ivorians and the descendants of immigrants from surrounding countries who formed 26%of the population.They were denied the right to vote and faced expoulsion from a country which was richer than nigeria until 1997 which they helped build.To this day ivorians and the immigrants live in tension.