Now what?

What they mean here is a little unclear. The situation is that your target (the Ottomans) is allied to someone you really don't want to fight. The solution is to attack one of their allies that you can fight, preferably someone small that will call the Ottomans into the war. During that war you separate peace your the Ottomans, but with the goal of taking money and forcing them to break alliances with any large powers that you don't want to fight. It is important not to push them over 50% warscore on the peace deal though. If you do that the peace could be longer than 10 years, and the Ottomans might be able to renew their alliance with the nations you don't want to fight.

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