 Complete the following phrase:  MacGregor joined the British Army at 16, the youngest age it was possible for him to do so, in April 1803. His family purchased him a commission as an ensign in the 57th West Middlesex Regiment of Foot, probably for around 450. MacGregors entrance to the military coincided with the start of the Napoleonic Wars following the breakdown of the Treaty of Amiens. Southern England was fortified to defend against a 