As though you needed an amendment to say that states may have armies. States have had armies forever before that was written.
I think the Founders pretty much meant that EVERY home should be able to take a few of the enemy out if attacked, before possibly being killed.
And more than a few is better.
Nothing harder than having to fight for EACH AND EVERY HOUSE or block when invading.
Armies have succeeded in doing this but at horrific prices.