The division into major and minor prophetic writings based upon the mere bulk of the books is unhistorical and non-chronological. Obadiah was the oldest of the prophets according to many scholars, prophesying in 887 BC, which was 127 years before Isaiah. The heathen nations were to rise up and destroy one of their own nations which was Edom. God uses the heathen to destroy his enemies. God permits the Devil to call some preachers, and these preach a false gospel to damn those who hate God.
Pride goes before destruction.
Pride caused Lucifer to sin against God. The day of restitution at hand. The day of the Lord is first mentioned by Obadiah and enlarged upon by the prophets Joel and Isaiah. Day of Christ or Son of Man. Day of Lord.