What caused three border states to stay in the union?

Three border states—Kentucky, Missouri, and Maryland—stayed in the Union during the Civil War primarily due to a combination of strategic significance, economic interests, and internal political dynamics. Their geographical locations were crucial for transportation and resources, making them vital for the Union's military efforts. Additionally, strong Unionist sentiments among their populations, as well as the influence of local leaders, played a key role in maintaining their allegiance to the Union despite their ties to slavery.