It was not symmetrical but the war was necessary to prove how asymmetrical it had become. Neither the election process, nor the census process were accurate enough to convey the situation in the Midwest. The population in the Midwest was larger, growing faster, more male dominated, and more anti-slavery, then either mechanism could show. The rate of family formation was very high.
The Midwest was growing because of east/west migration, international immigration, and south/north immigration. Not every man was naturalized and could vote, so the elections were not perfect reflections of the demographics.
Census procedures were not good enough to record the fast growing population, and they weren't published until May of 1862, and then again in 1864. And most people did not read them. When the Midwest states began to do school censuses in 1865 they discovered there had been a substantial under count in 1860. In 1866 the census commission took another look at the census numbers, particularly as to towns and cities, and then in 1870, a new census confirmed: the Midwest had overtaken the other two major sections of the country.
Under these circumstances, war, mobilization and the roster of regiments, was the best test of the relative strengths of the various sections.
The people in the west best able to observe what was happening were in Kentucky. They waited, and observed events in w. Virginia and Missouri. Much as they wanted to protect the status quo and slavery, they observed the reality that the Richmond government did not have the ability to protect slavery in Kentucky.
The secession crisis begins with 8 states in the western slave section of the US. Kentucky, Tennessee, Alabama, Mississippi, Louisiana, Texas, Arkansas and Missouri. There were only seven connected paid labor states, Ohio, Indiana, Illinois, Iowa, Minnesota, Wisconsin and Michigan.
But in the first six months after the bombardment of Fort Sumter, the test was presented: who was going to show up. And it turned out that w. Virginia had an Ohio economy. Regiments from Illinois and Iowa were rushing into Missouri and were willing to overcome any initial setbacks. As a result, the new state of Kansas was no longer separated from the rest of the US.
That gave Kentuckians the choice of seceding and having the war occur in Kentucky, or not seceding, and at least protecting their farms and towns, if not the long term viability of slavery.
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In less than six months, w. Virginia, Missouri, Kansas, Kentucky and the territory of Nebraska, were all solidly connected to the US.
And the Confederate state in the west with the largest white population, Tennessee, was also the state in which public opinion was the most deeply divided.
And that is just the west. In the coastal, maritime, trade economy of the east coast, in which steam vessels could go anywhere and strike where they wanted to, the imbalance was even greater.