Here's why:
* Early Anti-Slavery Advocacy: Seward was a prominent member of the Anti-Slavery Society in New York and a vocal opponent of slavery from his early political career. He believed it was a moral evil and a threat to American democracy.
* "Irrepressible Conflict" Speech: His 1858 "Irrepressible Conflict" speech famously declared that slavery and freedom were fundamentally incompatible, setting the stage for the Civil War.
* Senator and Secretary of State: As a US Senator, Seward was a leading voice for the Republican Party and its anti-slavery agenda. He supported the Kansas-Nebraska Act's repeal and helped to pass the 13th Amendment that officially abolished slavery. As Secretary of State under President Lincoln, Seward negotiated the purchase of Alaska, a move he saw as contributing to the expansion of freedom.
* Support for Emancipation: Seward was a strong advocate for the Emancipation Proclamation and saw it as a crucial step towards ending slavery and ensuring the Union's victory.
While Seward's personal views on slavery were clear, his actions and policies were sometimes met with criticism. Some historians argue that his emphasis on national unity and his willingness to compromise with slaveholders at times hindered the abolitionist cause.
However, there's no doubt that William Henry Seward was a committed abolitionist who played a significant role in the fight against slavery. His contributions to the cause are deeply intertwined with the history of the United States.