Hey there!
Let's analyze each of these. Many of these ended up boosting the economy, but only one lead to industrialism, or a big increase is manufacturing.
The Louisiana Purchase led to a lot of exploring and land trading, but not necessarily industrialization.
The revolutionary war gave the U.S. its independence but did not start any specific types of industries.
After the Mexican war, the U.S. gained more land in the West but for the same reason as the Louisiana Purchase, it did not increase manufacturing industries.
This leaves the answer as D) The War of 1812. The War of 1812 reinstated that the U.S. did not need to trade with Britain or many other countries, which led many states to begin to manufacture their own goods.
I hope this helps!
