In short
MRP II is an extended production planning approach that considers material planning together with capacity, labour, machine and financial resources.
Classic MRP focuses only on materials; MRP II also asks whether the plan is feasible: is there enough machine and labour capacity, and does the plan make sense financially?
MRP II brings sales and operations planning, rough-cut capacity checks, detailed capacity planning and shop-floor control into a single closed loop. This approach is also the predecessor of ERP systems.