Complex sentence: The deteriorating strategic situation forced France to increase its military commitments; in February 1808, Napoleon had boasted that 12,000 men could conquer Spain; by 1 June, over 65,000 troops were rushing into the country to control the crisis.
Split into simpler sentences: The deteriorating strategic situation forced France to increase its military commitments. In February 1808, Napoleon had boasted that 12,000 men could conquer Spain; by 1 June, over 65,000 troops were rushing into the country to control the crisis.