Explain how a bill passed in 1854 could be credited with sending the nation into civil war seven years later.

The bill that was passed in 1854, and which helped cause the Civil War to begin, is called the Kansas-Nebraska Act.  It was proposed by Senator Stephen A. Douglas (who opposed Abraham Lincoln in the Lincoln-Douglas Debates).  Its main immediate effect was to overturn the Missouri Compromise and allow people in the territories of Kansas and Nebraska to vote for themselves as to whether their territories should allow slavery.  This increased the amount of tension and hatred between the North and South and helped bring about the Civil War.
Before the Kansas-Nebraska Act, the Missouri Compromise had settled the issue of what parts of the Louisiana Purchase would allow slavery and which would not.  The Missouri Compromise had drawn a line across the Purchase.  Anything south of that line would have slaves and anything north of the line would be free.  The area that now makes up both Kansas and Nebraska was north of this line and was therefore going to be free territory.  This law was passed in 1820 and it helped keep the peace between North and South because it prevented any further conflicts over which areas would be slave and which would be free.
In 1854, Senator Douglas proposed a bill that would throw out the Missouri Compromise (follow the link below to read about why he wanted to do this).  Under the Missouri Compromise, both Kansas and Nebraska were free areas.  Under Douglas’s bill, this was called into question.  Instead of being free areas, these two territories would be up for grabs.  People in the territories would get to vote on the issue of slavery.
This helped lead to the Civil War in two main ways.  First, it helped to convince the North that the South had too much power.  Northerners feared the political power of the South and the Kansas-Nebraska Act did more to convince them that their fears were justified.  The South, they felt, had been able to overturn the Missouri Compromise, take land that had been free, and make it possible for slavery to be introduced there.  The North wondered what else the South might do with this power and it resented the idea that it had to fight again for land that had already been set aside as free soil.  By making the North resent and fear the South more than it had, the Kansas-Nebraska Act helped bring on the Civil War.
Secondly, the act brought about a period of violence in Kansas that we now call “Bleeding Kansas.”  Both North and South wanted to win when the people of Kansas voted on whether to allow slavery.  Therefore, both sides sent settlers into the area.  In addition, people within Kansas started to fight one another, hoping to drive the opposition out of the territory before the vote.  Terrible atrocities were committed by both sides.  This was the first really serious violence over the issue of slavery.  Of course, having people killing each other over this issue made both the North and the South hate each other more.
In these ways, the Kansas-Nebraska Act helped bring on the Civil War.  It did not cause it to happen immediately, but it increased the amount of hatred and distrust between the two regions of the country.  This is how a bill passed in 1854 could help lead to the start of the war seven years later.
https://www.history.com/topics/19th-century/kansas-nebraska-act