This phrase was included in the Preamble to the Constitution to ensure a military that could protect our country. "secure the Blessings of Liberty to ourselves and our Posterity" "insure domestic Tranquility" "provide for the common defence" "establish Justice"

"provide for the common defence" would be the phrase that was included in the Preamble to the Constitution to ensure a military that could protect our country. Although we take it for granted today, it was not ensured for some time that there would be a military.