Short answers, pulled from the story.
The First Battle of Changsha took place from the 17th of September to the 6th of October 1939. Its opening came roughly two weeks after Germany's invasion of Poland on the 1st of September, making it one of the first major engagements of World War II.
Japan attacked Changsha to restore military morale after a defeat at Nomonhan by Soviet forces and the destabilizing effect of Germany's non-aggression pact with the Soviet Union. A decisive victory against China was also intended to support the establishment of Wang Jingwei's puppet government in Central China.
General Chen Cheng ordered his forces to lure the Japanese toward Changsha rather than defend each position along the way. Chinese forces applied scorched earth policies, evacuated civilians, and relied on guerrilla-style ambushes designed to exhaust Japanese manpower and cut their supply lines.
The Japanese force converging on Changsha numbered around 100,000 men, drawn from six divisions: the 101st, 106th, 3rd, 6th, 13th, and 33rd Divisions. Naval forces, including the Shanghai Special Naval Landing Forces, also participated.
Japan officially claimed 850 killed and 2,700 wounded, while also claiming to have inflicted 44,000 Chinese deaths and 4,000 captures. Foreign military observers estimated roughly 30,000 Japanese casualties and around 20,000 Chinese killed and wounded. Military historian Micheal Clodfelter placed total Japanese casualties at around 50,000.
The First Battle of Changsha was the first time a major Chinese city successfully repelled a Japanese advance during the Second Sino-Japanese War. Holding the city prevented Japan from consolidating control over southern China. Japan would make three more attempts to take Changsha before the war ended.