In the US, the National Minimum Drinking Age Act of 1984 required that if a state allowed anyone under the age of 21 to drink then their Federal highway appropriation would be reduced by 10%.

The law has been amended multiple times since and was last amended in 2012 to reduce the appropriation reduction to 8%.

There are a number of similar questions and responses in the past.

In general, legal drinking ages are the result of pushes either by temperance movements (which is when you start to see both stricter licensing acts and drinking ages come in in the late 19th century) or (as in the case of the 1984 act) political pushes to remove societal threats. In the 1984 case Mothers Against Drunk Driving lead the push to increase the drinking age to reduce the number of drink driving fatalities.