Imperial trade restrictions and merchant shipping

Shipping was imperial infrastructure: colonies needed enough merchant hulls to move goods and sustain connections with the metropole. Spain restricted colonial commerce to Spanish trade but did not provide sufficient shipping, then diverted scarce vessels to patrol duties. Britain took a different approach by continually building general-purpose merchant ships that could carry varied cargoes and connect distant parts of its empire. Restrictive trade rules became brittle when the home country could not provide the transport capacity its colonies needed.