How do we know that all men are sinners because of Adam?

Romans 5:12 clarifies that through Adam's singular act of sin, death entered the world, and this sin is imputed to all men, making them sinners. Theological tradition understands Adam as both a common head and a federal representative of mankind; hence, his disobedience rendered all his descendants guilty of sin. This doctrine underscores the historical and theological connection between humanity's state before God and the consequence of Adam's fall, establishing the need for salvific grace through Christ as the remedy for this inherited sin nature.