 However, other sources claimed the Dutch's Cultivation system is linked to famines and epidemics in the 1840s, firstly in Cirebon and then Central Java, as cash crops such as indigo and sugar had to be grown instead of rice.Furthermore, the age of first marriage dropped during the 19th century thus increasing a woman's child-bearing years.Indonesian nationalism first took hold in Java in the early 20th century, and the struggle to secure the country's independence following World War II was centered in Java.