I also wanted to add that I was in keep 6, and I had 0 crowns. When I first started to attack it looked like it would take forever to reach the 100 crowns (and 2000 crowns for the other achievement) as I was only getting 2 crowns per win. After I hit 50 crowns it skyrocketed and my next win I got 21 crowns, next 19, next 23 and so on. So do not give up just because it looks like you are getting no crowns each win.
Also for this achievement I believe only crowns won on offense count, not defense.