The 1860 Federal census states that there were over 27,489,000 total free persons in the United States. Of those over 4,100,000 were born outside of the United States. That means over 15% or 1 out of 6.7 people were foreign born free persons.

That means that the Battle of Gettysburg would have been fought by nearly 14,000 foreign born Union troops against 10,754 foreign born Confederates-- using the averages.

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David Upton