Wider co-operation between the Habsburgs was limited, since their objectives did not always align; Spain was a global maritime power, Austria primarily a European land power, focused on the Empire, which contained over 1,800 members, most extremely small. Although a Habsburg had been Holy Roman Emperor since 1440, their control over the Empire was weakened by the 1555 Peace of Augsburg, and this continued in the period leading up to 1620. Reversing this was a key factor behind Austrian involvement in the Thirty Years War; the 1648 Treaty of Westphalia accepted this had failed.