Kungumam

Sundharam (Sivaji Ganesan) loves Gomathi (C. R. Vijayakumari), where the latter is an orphan and lives with her uncle's family. Sundharam leaves to the United States of America for further studies. When Sundharam comes back four years later, he was shocked to see that his mother Vedhavalli (M. V. Rajamma) as a widow and was told that his father Sambasivam committed suicide due to of disgrace that unable to pay back the loans.
Sundharam leaves to Bombay for an interview where comes across a murder of broker Govindan tooks place and shocked to see that the murderer is Punniyakodi (S. V. Ranga Rao) who is later introduced as Gomathi's father in a police investigation. Sundharam helps Punniyakodi to escape and in turn is suspected by the police as the culprit instead. Police Superintendent Raja (S. S. Rajendran) is appointed to investigate the murder case. When Gomathi's uncle refuses to let her getting married to Sundharam, she leaves home following Vedhavalli to Madurai. Sundharam travels back to Madras where he bumps into Suseela (Sharadha) on the road. Sundaram finds Govindan's family and offers help who initially refuses but later accepts when persuaded and explained. While leaving Gobvindan's house, Sundharam learns that Punniyakodi is living as a fugitive had changed his name as James and staying with a crook Kandhan (O. A. K. Thevar). Sundharam seeks his friend Dhas (R. Muthuraman) help in taking care of Punniyakodi for the time being and goes to Madurai and explains to Vedhavalli and Gomathi that he is a murderer and wanted by the police but Vedhavalli refuses to accept Sundharam as her son due to the conviction.
Sundharam upon reading an advertisement in the news paper, joins as a tuition teacher in disguise as Kalamegam. There Sundharam learns that Suseela's father is Justice Somanathan (S. V. Sahasranamam), her cousin is Inspector Raja, servants Arasan (Nagesh) and Kanniamma (Manorama). Meanwhile Superintendent Raja hatches a plan to move Vedhavalli and Gomathi to Dhas's house so that to ease to capture Sundharam if he happens to visit them but James leaves Dhas's home following Kandhan's temptation. Suseela refuses Raja's advances and develops a soft corner for Kalamegam but later finds out that he is Sundharam and his deeds but lies to Justice Somanathan that he is a good man. Suseela also lets Sundharam escape when Raja finds out about this.
Vedhavalli who is a staunch believer of justice, hates Sundharam for his conviction and arranges Gomathi to be married to Dhas but Gomathi refuses. In turn Gomathi pleads Sundhram to marry Suseela as Suseela had help them out a lot to prove Sundharam's innocence before gets shot by the police mistaken for Sundharam. A trial takes place where Sundharam accepts the all the charges onto him. A twist in the story occurs when Somanathan produces Punniyakodi and Kandhan in court. Punniyakodi admits in court that he is cheated by Kandhan into shooting broker Govindan where Kandhan earlier had told Punniyakodi that by the revolver is unloaded. Lastly Punniyakodi admits that he is actually Sambasivam and was introduced as Punniyakodi to the police by Sundharam who was only doing all these in order to save him. The judges sentences Kandhan for murder, further trials for Sambasivam and 6 months for Sundharam. At the end of the story, Sambasivam applies kungumam to Vedhavalli at the request of Sundharam.

Question: Why does Sundharam leave the United States?
Answer: further studies