"to keep him from going into the Low Country wars"
The Surrender of Breda, 1635
Public DomainThe Surrender of Breda, 1635 - Credit: Diego Velázquez

The "Low Country wars" were the Dutch Wars of Independence, also known as the Eighty Years War, which lasted from 1568 to 1648.  The Habsburg Netherlands were under the control of Spain, until seven provinces seceded to form the Dutch Republic.  Two more, Flanders and Brabant, would later become Belgium.  Cromwell's Protestant England supported the rebel provinces against Catholic Spain. 

The war was ended, together with the more wide-ranging and destructive Thirty Years War, by the Treaty of Westphalia (1648).