Late in 1930 and early in 1931 a menacing alliance was organized between two of the most influential remaining Northern _tuchüns_ and the "liberal" wing of the Nationalists. Operating from the north, after the proclamation of an insurgent "National Government" at Peking, the rebels at first seemed to have the military advantage. Chiang had learned many lessons, however, and in the most serious fighting which China had seen in years he broke the force of the Northern offensive. Airplanes appeared as a threat against the civilian population of Peking, although no actual deaths were reported. There were ugly rumors that gas was being used at the front. Small tanks from England, though giving a rather poor performance, symbolized a novel trend. More and better heavy artillery was used than ever before. Trenches came up to World War standards. The war ended with the intervention from Manchuria of Chang Hsüeh-liang, a strangely progressive and patriotic _tuchün_; but the fighting had been enough to show that of all the great armed forces in China the Nationalist armies of Chiang K'ai-shek and the Nanking government were the most effective. The rehabilitation of men's thinking had not proceeded far enough to eliminate the dangers of an overemphasized military leadership, but the tide had turned. After 1931 the military situation in China had become subordinate to the problems of ideology and of government. The chief military factors were now the governmentalized armies, the guerrilla opposition of the Communists, and the problem of foreign war. _The Age of Air Conquest_ The new military period which replaced the war-lord system was marked by (1) technical improvement of the armies, especially in the direction of air power; (2) supplementation of the armies by the quasi-military power of the civil government, so that Chinese wars ceased to be a question of armed bands drifting about the surface of the social system; (3) organization of the Nationalist armies into national units in fact as well as name; (4) increasing pressure of the disbandment problem; (5) development of guerrilla tactics by the Reds and of guerrilla-suppression tactics by the Nationalists; (6) problems arising from Japanese conquest, which overwhelmed Manchuria in one fierce onslaught and harassed China for six years of military aggressions before breaking forth anew in the catastrophic surge of 1937-1938.