A 1625 treaty formed a secret alliance to challenge the Spanish Empire's global dominance

The 1625 Treaty of Southampton established a high-stakes military alliance between England and the Dutch Republic during the early years of the Thirty Years' War. Both nations were desperate to curb the overwhelming global influence of the Spanish Habsburgs, who dominated the seas and the American colonies. This agreement committed the two powers to a joint naval campaign, leading to a massive but ultimately disastrous expedition against the Spanish port of Cadiz.