Yes, state militia service was mandatory, but that’s a different issue. The fact that some states during the Revolution essentially conscripted people into state military units does not mean that the U.S. Constitution gives the Federal Government a conscription power. Absent a conscription power, the Tenth Amendment bans federal conscription. Tom and I have a chapter on this subject in our book Who Killed the Constitution? The two-year limitation means the Congress cannot raise a perpetual army, which was a European practice dangerous to parliaments’ power.