French troops could help train an Imperial Mexican Army larger than the force France could deploy. They would also form the core of a mobile force and hold strategic positions, making an attack risk war with France. Such a war is imagined as costly and inconclusive, comparable to a more technologically destructive War of 1812. American defeat would not be necessary to make intervention unattractive. During Reconstruction, Washington would have reasons to avoid a European enemy able to supply rifles to disaffected people in the South. The deterrent therefore depends on the expected cost of another war while the United States is trying to recover from its civil war.
Notable Point · 58:23-1:00:22
Why a war with France could deter postwar America
The deterrent rests on the costs of another major war during Reconstruction, without assuming that France would defeat the United States.