See the history of US taxation. Before World War I it almost zero (1% to 7%), and when it came it skyrocketed. 

According to Investopedia: "The first estate tax was enacted in 1797 in order to fund the U.S. Navy. It was repealed but reinstituted over the years, often in response to the need to finance wars. The modern estate tax as we know it was implemented in 1916. "

Maybe they found war a good excuse to get more money!
On top of that, armaments industry has also to make lobbying to get funding, and no one will buy armaments without a good old war.

Related articles:
https://www.investopedia.com/articles/tax/10/history-taxes.asp
https://en.wikipedia.org/wiki/History_of_taxation_in_the_United_States