China's early demographic history is similar to that of Europe; population grows only slowly due to war, disease and Malthusian resource limitation. Later, introduction of American foods allowed cultivated land to expand, but population expanded even more rapidly, leading to an extremely dense, but poor population. During this time, female infanticide was frequent, but almost all surviving girls got married. Within marriage, their fertility rate was much lower than that of their European counterparts. This system compares to the English with a low rate of marriage, but high fertility within marriage.