But Fate was too strong for schismatic tradition, and the two worlds had merged into one. The shrinking of space and expansion of mind was abolishing East and West, and the two hemispheres had become one exchange and mart of commodities and ideas. They could not continue to revolve on diverse political axes, and neither was safe without the other's concurrence. To the German cry of weltmacht must sooner or later respond the American cry of weltrecht; for the war was a civil war of mankind, and upon its issue would hang the future of human government. Intervention was inevitable, not so much because the Kaiser had said he would stand no nonsense from America as because, if America was to stand no nonsense from him after victory, she would have to turn the New World into an armed camp like the Old and run the same race to ruin. The old peace and isolation were in any case gone, and the choice was between war for the time, with the prospect of permanent peace on the one hand, and peace for the time, with the permanent prospect of war on the other. There was no other way, and Germany forced the American people to realize their dilemma.
President Wilson had seen it earlier than the majority of his fellow-countrymen; but for a statesman a vision of the truth is an insufficient ground for acting upon it. He is bound, indeed, not to act upon it until he can carry with him the State he governs; otherwise he ceases to be a statesman and sinks or rises into the missionary. The zealot is ever ready to break his weapon upon the obstacle he wishes to remove, but the statesman who destroys national unity in his zeal for war does not help to win it; and American intervention was both useless and impossible until the President could act with his people behind him. Nor, as official head of the State, could he play the irresponsible part of an advocate; if he believed war to be inevitable in his country's interests, it was for him to convince the people not by argument, but by his conduct of American affairs. Idealism entered more largely into his policy than that of most statesmen, but it was bound to American mentality and national interests; for ideals which do not affect national interests do not appeal to the majority in any nation, and the lawlessness which trampled on Belgian neutrality made less impression across the Atlantic than that which destroyed American lives and property.
A subsidiary cause of delay in American intervention was the absorption of the United States in the presidential contest of 1916, but President Wilson's re-election in November gave him a freer hand than was possessed by any other democratic statesman. No American president is ever elected for a third term of office, and Mr. Wilson had no need to keep his eye on his prospects for 1920. He must, indeed, secure the assent of Congress before war could be declared, but in both Houses his party had secured a majority in November. The decisive step was not, however, taken by President Wilson, but by the German Government, and America was as much forced into war in 1917 as we were in 1914; and in both cases it was their view of military necessity which drove the Germans into political suicide. They could not, they thought in 1914, cope with Russia until they had first beaten France, and they could not beat France in time unless they trampled a way through Belgium. So in the early days of 1917, not foreseeing the fortune which the Russian revolution was to bring them, they saw no prospect of victory save through the ruin of England by means of their submarines. The Eastern and Western fronts were too strong for a successful offensive against either, the military situation was growing desperate, and their offers of peace had been scorned; the war went on in their despite, and their real offensive for 1917 was the submarine campaign. It was adopted because there was no opening on land and no hope of success in a naval battle; and its adoption justified those who held that the remedy was worse than the disease and that unrestricted submarine warfare would bring the United States into the war before it drove Great Britain out.
As late as 22 January, President Wilson, while depicting the sort of peace which would commend itself to the American people, disavowed any intention of helping to secure it by force of arms. But on the 31st Germany revoked her promise given on 4 May 1916 that vessels other than warships would not be sunk without warning, and announced her resolve forthwith to wage submarine war without any restriction. Later on Herr Bethmann-Hollweg stated that the promise had only been given because Germany's preparations were incomplete, and was revoked as soon as they were ready. The President's answer was prompt: on 3 February the German ambassador was given his passports and Mr. Gerard was recalled from Berlin. But the invitation to other neutrals to follow the President's lead was declined on this side of the Atlantic. Switzerland, without any seaboard, was not concerned with submarine warfare, and other neutrals were too much under the influence of German blandishments or terror to risk war in defence of their rights; they preferred to abandon their sailings to British ports.
At first the President contemplated no more than an armed neutrality, and proposed to equip all American mercantile vessels for self-defence. But the sinking of American ships and loss of American lives began to rouse popular anger; sailings stopped at the ports, the railways became congested with goods seeking outlet, and the remotest inland districts felt the effects of the German campaign. In March, too, the Russian revolution removed a stumbling-block to co-operation with the Entente, for American public opinion had always been sensitive to the iniquity of the old regime in Russia. At length the President summoned a special session of Congress, and on 2 April recommended a declaration of war. It was adopted in the Senate on the 4th by 82 votes to 6, and by the House of Representatives on the 5th by 373 to 50. Of the ultimate issue of the war there could now be no doubt. Time would be needed for the United States to mobilize its resources and train its armies, and the extent to which they might be required would depend upon the course of events in Europe. But the Americans were not a people to turn back having put their hand to the plough, and with their forces fully deployed they would alone be more than a match for the German Empire. Victory might be delayed, but its advent was assured, and the first fortnight of April saw the hopes of the Allies rise higher than since the war began.