Final answer:
Britain justified its interference with American commerce primarily based on the need to strengthen its naval forces during the conflict with Napoleon, resorting to practices like impressment and the Prohibitory Act to bolster its navy.
Step-by-step explanation:
The argument that Britain might have made for its many acts against American commerce on the seas primarily revolved around their naval requirements during the time of the Napoleonic Wars. The British Royal Navy engaged in 'impressment' of American sailors to supplement their forces, a practice of forcing them into British service. The Prohibitory Act of 1776 was one of the measures taken during this period, warning American vessels of potential confiscation.
Britain's actions were not necessarily a desire for war with America but rather a reflection of the needs of the British navy to sustain its strength against Napoleon. The American response, such as the Embargo Act of 1807, sought to exert economic pressure on Britain and France to halt their interference with American shipping, though it severely impacted American commerce instead.