It was a different time. Today, people dial 911, and wait for the police to arrive. Back then, if a local brave got irate and gathered together a war party to attack settlers, they didn't dial 911. The local militia grabbed their muskets and defended their homes. No one was coming to rescue them. Not in time anyway.
The writers of the Constitution didn't believe in a strong standing army. When the War of 1812 started, the US had few troops ready to meet it. Only the fact that Britain's main army was engaged fighting Napoleon prevented them from recapturing major US cities. Even so, the British captured DC, and zapped the White House. The strategy back then really was to depend on local militias to resist tyranny long enough for a new army to be trained and equipped.
Fortunately for the US, Britain decided to make friends with America after their experience of trying to simultaneously fight in Europe and America. They decided that preventing Europe from uniting into a power that could threaten them was more important than retaking their former colonies. They adopted a deliberate policy of friendship with the USA, which bore fruit for them when the US came to their rescue in WWI and WWII.