After the signing of the armistice, Wilson traveled to Europe to lead the American delegation to the Paris Peace Conference, thereby becoming the first U.S. president to travel to Europe while in office. Senate Republicans and even some Senate Democrats complained about their lack of representation in the American delegation, which consisted of Wilson, Colonel House, Secretary of State Robert Lansing, General Tasker H. Bliss, and diplomat Henry White. Save for a two-week return to the United States, Wilson remained in Europe for six months, where he focused on reaching a peace treaty to formally end the war. Wilson, British Prime Minister David Lloyd George, French Prime Minister Georges Clemenceau, and Italian Prime Minister Vittorio Emanuele Orlando made up the "Big Four," the Allied leaders with the most influence at the Paris Peace Conference. Wilson had an illness during the conference, and some experts believe the Spanish flu was the cause.