Pressure grew on Spanish minister Olivares to make peace, especially after attempts to hire Polish auxiliaries proved unsuccessful. Cutting the Spanish Road had forced Madrid to resupply their armies in Flanders by sea and in October 1639 a large Spanish convoy was destroyed at the Battle of the Downs. Dutch attacks on their possessions in Africa and the Americas caused unrest in Portugal, then part of the Spanish Empire and combined with heavy taxes caused revolts in both Portugal and Catalonia. After the French captured Arras in August 1640 and overran Artois, Olivares argued it was time to accept Dutch independence and prevent further losses in Flanders. The Empire remained a formidable power but could no longer subsidise Ferdinand, impacting his ability to continue the war.