How does Achebe use Okonkwo's breakdown to reflect the tribes' falling apart in the novel, Things Fall Apart?

Firstly, Okonkwo is used as a symbol for the society he represents. He is a strong, powerful man, intolerant, one who despises weakness and laziness. He is strict, commanding and demanding. He has certain foibles which can be seen as both weaknesses and strengths: he is too proud but not boastful and he applies his rules with too firm a hand. We read about him in chapter 1:

He was tall and huge, and his bushy eyebrows and wide nose gave him a very severe look. He breathed heavily, and it was said that, when he slept, his wives and children in their houses could hear him breathe. When he walked, his heels hardly touched the ground and he seemed to walk on springs, as if he was going to pounce on somebody. And he did pounce on people quite often. He had a slight stammer and whenever he was angry and could not get his words out quickly enough, he would use his fists. He had no patience with unsuccessful men.

Okonkwo ruled his household with a heavy hand. His wives, especially the youngest, lived in perpetual fear of his fiery temper, and so did his little children. Perhaps down in his heart Okonkwo was not a cruel man. But his whole life was dominated by fear, the fear of failure and of weakness

All of these qualities are a reflection of Ibo society itself.

It is these qualities which eventually lead to Ibo society falling apart and Okonkwo's downfall reflects the destruction of what held Ibo society together. When the strength of a society falters or when its will is broken, it will weaken and lose its identity. 

Okonkwo resisted the invasion of his society by the missionaries and the colonialists from the outset. He willfully disobeyed their rules and refused to budge. He fought against all their attempts to dominate him and bow to their authority, but it was his persona, epitomised by his pride and recalcitrance, which gradually gnawed away at his power and, in effect, weakened him.

Ibo society was just as proud of its culture and traditions, but once the missionaries and the colonialist government started spreading their influence, it, in turn, gradually eroded the basic principles which held Ibo society together. When some members of the tribe turned and adopted the principles of the new religion, the central structure broke down - new beliefs and habits were adopted and the old ones were either ignored or abandoned completely.

Okonkwo, in a similar fashion, was disobedient to the tenets of his culture. When he, for example, beat his wife during the Week of Peace, he had disobeyed culture and he was punished for it. When he shot dead the son of an elder during his funeral, even if it was accidental, he broke a fundamental law and was severely punished for it. He was banished to his mother's village for seven years. In that time, he lost contact with his village and he was not there to make the stern demands required of the villagers to resist the foreign influence that had come to infest his society. None of the other villagers were as forthright and brave as he. This led to a number of them accepting the new authority and the new religion. Okonkwo's failure, in this regard, became the failure of Ibo society.

Two of Okonkwo's greatest strengths were also his greatest weaknesses: his pride and his fear of failure. This is best illustrated with the death of Ikemefuna, a boy left in his care. He was too proud and afraid of being called weak when he cut the boy down himself for he believed that that was what a great and powerful man should do. Although he was overcome by remorse and isolated himself for two days, the damage had been done. His son, Nwoye, turned from him and became a member of the new religion later.

The fact that he was afraid of showing weakness and feared failure, resulted in Okonkwo adopting a very harsh attitude towards what he believed were outsiders (which they were) trying to forcibly impose their will upon him and his people. They burned the church down and were sanctioned for their crime. Okonkwo was unforgiving and relentless. He killed one of the messengers and was sought for arrest and punishment but he had disappeared. His body was eventually found hanging from a tree after he had committed suicide.

Okonkwo refused to be dominated by those he believed had no authority over him and his pride made him choose suicide rather than to be humiliated by the punishment of those he despised. His death, which was seen as an abomination, indicates his determination to not be cowed into submission. There was more honour in taking his own life, even though it meant eternal damnation, than to submit to the will of outsiders.

It was this same approach by other members of his tribe which eventually led to its breakdown. Many of them refused to be obedient to the new laws and they were punished for their defiance. In the end, their incarceration, displacement or execution led to a lack of leadership and they, who were the centre, could not maintain a grip on their people and resist the invaders. In the end, because the centre could not hold, things fell apart.