Cymbeline, King of Britain Patriotism Quotes

How we cite our quotes: (Act.Scene.Line)

Quote #10

SOOTHSAYER
To the majestic cedar joined, whose issue
Promises Britain peace and plenty. (5.5.556-557)

For years to come, Britain will prosper. That's a cool way of ending the play, at least as far as the king is concerned, so why does he agree to pay the fee to Rome, then? Cymbeline just won the war, and he knows his country will flourish. What's the deal with agreeing to the tribute? Is it to ensure peace for the future?