Did you have a lot of buildings and units waiting to be produced?
When you got the 18k they all began producing at the same time.
Go check your provinces and see if there aren't a lot of buildings that are one year into production.

You don't drag your troops onto a ship. You form a chain of ships to the target province. Then you drag your troops there. But beware, any other ship, even an ally will interupt this.

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BTW, Danish Crusades are true to history.

You may not care about war, but war cares about you!