Complex sentence: In Madrid, the Spanish resisted the French occupation, leading the Portuguese to call on British support; and so, in August 1808, Wellesley entered the Peninsular War with 15,000 men.
Split into simpler sentences: In Madrid, the Spanish resisted the French occupation, leading the Portuguese to call on British support. In August 1808, Wellesley entered the Peninsular War with 15,000 men.