Due to the underlying pressure against military involvement by both citizens and politicians, the United States was reluctant to intervene in any overseas conflicts. The involvement that the United States had toward the Japanese Invasion of Manchuria in 1931 only extended as far as non-recognition. Other events such as Benito Mussolini's Italian Conquest of Ethiopia went ignored by the U.S. along with the League of Nations being unable to act upon the usage of chemical weapons by the Italian fascists. No official involvement was waged during the Spanish Civil War and the Second Sino-Japanese War, though both wars utilized loopholes for U.S. involvement, such as volunteering and using British ships as a middleman for delivering provisions (since the Neutrality Acts only specified American ships). This, along with Roosevelt's Quarantine Speech, produced mixed opinions among Americans that were still anxious about military involvement. Non-interventionists were mainly constituent in the Republican Party, but other Democratic politicians, such as Louis Ludlow, attempted to pass bills to compromise and even amend the United States Constitution for the purpose of calling for public Referendum to decide military involvement in cases that do not immediately follow an attack on the United States. This amendment was introduced many times, but failed to gain enough support, including opposition even by Roosevelt.