What measures did the north take to cripple the south's economy?

The naval blockade - it took some time to implement, but it was highly effective.

Refusal to trade with the South - so the South had to depend on the Confederate dollar, which became worthless.

Punitive raids on Georgia, South Carolina and the Shenandoah Valley - wrecking the farms and railroads, and helping to starve the enemy troops in the field.