Complex sentence: He entered the army as second lieutenant in the Ninth Infantry in July 1799, was transferred to the artillery, and in May 1808 organized and commanded the first light battery of artillery in the country.
Split into simpler sentences: He entered the army as second lieutenant in the Ninth Infantry in July 1799, was transferred to the artillery. Later in May 1808 Peter organized and commanded the first light battery of artillery in the country.