Actually, the role of women is quite complicated in the Ibo culture. Although it is true that women could not hold the same positions in the tribe as men, they had a very important place in the social structure; as the previous poster mentioned, they were the backbone of the domestic sphere. It is also important to note that this is essentially the same role women had in Western countries at the time, & that spousal abuse was not necessarily frowned upon in those nations either.
It is clear that women had rights in this culture as well. For example, during the trial of the women who left her husband, she is found to have been in the right. He is the one punished for having beaten her repeatedly during their marriage. Okonkwo too is reprimanded for his treatment of his wives, and when he beats his wife during the Week of Peace, he is publicly humiliated and told he has committed a great evil.
Finally, the Ibo worship both masculine and feminine deities. Those who do not respect the feminine aspect of their spirituality (such as Okonkwo) are punished, and looked down upon by the village. Indeed, one of the most powerful members of the community is Chielo, a priestess of Agbala. Although she is female, no man can order her because of her status. Her religious role has elevated her to equality with men, perhaps even surpassing them. Thus, although there is much abuse in Things Fall Apart, it is not necessarily a result of the Ibo culture.
Chinua Achebe's Things Fall Apart takes place in pre-colonized Nigeria. Women were less than secondary class citizens. Their chief role in life was to bear children, hopefully males, and to serve their husbands at all times. However, they did have a role: to take care of the children, especially the girls, be submissive to their husbands, and to take care of house duties. Abuse was just part of the norm, unfortunately.
During that time, although women were considered important in some parts of society they were mostly considered inferior to men. For example, they were more used for child bearing, cooking, cleaning. In the book, women and men would even grow different crops. For example, the yam was considered the crop for men, while cocoa beans were for women.