The best response to the question regarding why the Founding Fathers included the phrase "insure domestic Tranquility" in the Preamble to the United States Constitution is:
A because England's policies sometimes caused citizens to fight with each other.
This option reflects the historical context in which the Founding Fathers operated. The grievances against British rule included conflicts that arose from various policies, leading to unrest among citizens. The phrase emphasizes the intention to create a stable and peaceful society within the new nation.