Final answer:
The French and Indian War, which ended in 1763 as part of the Seven Years' War, caused England to accumulate a large war debt, leading to the imposition of new taxes on the American colonies and increasing tensions that contributed to the Revolutionary War.
Step-by-step explanation:
The war that caused England to spend a lot of money defending the colonies was the French and Indian War, which concluded in 1763. This conflict was part of the larger Seven Years' War and left Britain with a substantial war debt. In an effort to manage this debt, Great Britain imposed new taxes and strengthened enforcement of imperial trade laws, hoping to raise revenue from the North American colonies. Unsurprisingly, this led to significant discontent among the colonists, who resisted these fiscal pressures and asserted their stance with the prominent slogan, "no taxation without representation". Several colonies also refrained from contributing to the war expenses due to either economic hardship, pacifist beliefs, or lack of direct threat to their borders.
The British expected the colonies to contribute their fair share towards the war's expenses, but were met with resistance. This difference in perspectives, with Britain seeking gratitude and financial contribution from the colonies, and the colonies feeling that they had supported the mother country sufficiently, exacerbated tensions. The economic impact of the war and subsequent policies contributed to the strained relationship between Britain and its colonies, ultimately leading to the Revolutionary War.