The document discusses two main causes of US involvement in WWI: the sinking of the Lusitania by a German U-boat in 1915, and the economic opportunities for US businesses and industries from exporting goods to Europe. The sinking of the Lusitania, which killed over 100 American passengers, outraged public opinion in the US and pushed the country towards entering the war. US business owners also saw joining the war as a chance to profit from increased overseas demand and sales.