 This severed the Spanish Road, forcing Spain to reinforce their armies by sea, where the Dutch had maritime supremacy; in 1639, they destroyed a large supply convoy at the Downs.They also attacked Portuguese possessions in Africa and the Americas, then part of the Spanish Empire; Madrid's inability to prevent this caused increasing unrest in Portugal.Throughout the 1630s, attempts by the Crown of Castile to increase taxes and centralise control led to protests; in 1640, these became revolts in Portugal and Catalonia.