In Risk, if you want to start a war with a territory and the defender has a clavary piece there?

Question

a calvary piece is worth five units which is more than enough. What do you do if there are no more single unit pieces left to trade with the calvary piece?

Answer 1

If available, use the units from a color that is out of the game.

Answer 2

AS I remember the rules, there is a limit to the amount of pieces that can be used in the game.... so you can't have 2000 armies...

   But, if you need to break  a unit down to a smaller denomination you you could use pennies for 1 army, nickles for 5 armies, dimes for 10, and quarters for 25.