In general poorer nations will contribute troops to the UN rather than monetary payment for their membership.
Pakistan is the largest troop contributor followed by Bangladesh and then Nigeria.
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Desert Storm had America at the lead, not the UN. A UN led force will see the surrounding arab nations contribute the lions share of troop strength. None of Iraq's neighbors want that place to be destabilized for any period of time, and they will rightfully fear a dictator grabbing power from the weak government we set up. It will be in their own best interest to contribute to the nations stabilization.