To the cynic, two nations clasped in murderous embrace yet nominally living in peace with each other might well be one of the miracles of our century. No less miraculous has been for many the tenacity of Chinese resistance to Japan's invasion ever since the first bullets whizzed through the night near the Marco Polo Bridge southwest of Peking early in July, 1937. The undeclared war has spread disaster through an area larger than that immediately affected in Europe's battles from 1914 to 1918; hundreds of thousands have died in action; for months China's capital has been in the hands of the enemy. But China is not on her knees. The explanation is simple. For the first time in her history, China fights as a nation.