gain independence from Spain. President McKinley signed the joint resolution on April 20, 1898, and the ultimatum was sent to Spain. In response, Spain severed diplomatic relations with the United States on April 21. On the same day, the U.S. Navy began a blockade of Cuba. On April 23, Spain reacted to the blockade by declaring war on the U.S. On April 25, the U.S. Congress responded in kind, declaring that a state of war between the U.S. and Spain had de facto existed since April 21, the day the blockade of Cuba had begun. It was the embodiment of the naval plan created by Lieutenant Commander Charles Train four years ago, stating once the US enacted a proclamation of war against Spain, it would mobilize its N.A. (North Atlantic) squadron to form an efficient blockade in Havana, Matanzas and Sagua La Grande. The Navy was ready, but the Army was not well-prepared for the war and made radical changes in plans and quickly purchased supplies. In the spring of 1898, the strength of the U.S. Regular Army was just 24,593 soldiers. The Army wanted 50,000 new men but received over 220,000 through volunteers and the mobilization of state National Guard units, even gaining nearly 100,000 men on the first night after the explosion of USS Maine. Historiography The overwhelming consensus of observers in the 1890s, and historians ever since, is that an upsurge of humanitarian concern with the plight of the Cubans was the main motivating force that caused the war with Spain in 1898. McKinley put it succinctly in late 1897 that if Spain failed to resolve its crisis, the United States would see "a duty imposed by our obligations to ourselves, to civilization and humanity to intervene with force." Intervention in terms of negotiating a settlement proved impossible—neither Spain nor the insurgents would agree. Louis Perez states, "Certainly the moralistic determinants of war in 1898 has been accorded preponderant explanatory weight in the historiography." By the 1950s, however, American political scientists began attacking the war as a mistake based on idealism, arguing that a better policy would be realism. They discredited the idealism by suggesting the people were deliberately misled by propaganda and sensationalist yellow journalism. Political scientist Robert Osgood, writing in 1953, led the attack on the American decision process as a confused mix of "self-righteousness and genuine moral fervor," in the form of a "crusade"