The federal government prior to 1913 was a very small entity compared to today. Its primary funding sources were customs duties on exports and excise taxes on alcohol. If it wanted additional funds, its only Constitutional option was to levy an assessment on the states in proportion to their populations ("direct taxes"), which wouldn't go over well with the state legislators unless it was a critical and very temporary need. The feds could not support a large standing army, nor legions of "enforcement" troops, and so had little power to enforce their power on individuals
Then the income tax opened the door by handing independent funding to the feds. Conveniently, the feds got to exercise that funding authority almost immediately by getting us into WWI (which lead directly to the Bolshivek Revolution and indirectly to WW-2).
Giving the UN an independent funding source will lead directly to a UN military