Was the Civil war inevitable?

No war is inevitable, so no, the Civil War was not inevitable and not the only way the crisis over slavery could have been resolved. Proponents of slavery, for example, could have more readily acknowledged what most people understood: that labor-intensive agriculture was giving way to the industrial revolution. They could have been willing to work with the North and start taking proactive steps to begin dismantling slavery and switching to a machine economy in a way that would have been less shattering and painful than losing a war. Whether that would have been better or worse for the enslaved is an open question, but war was not the only answer.
Slavery has sometimes been compared to the so-called automobile culture that is changing the climate of the planet. Overwhelmingly, people who have studied the science have agreed that climate change is human-made and that we must move away from fuels that spew carbon dioxide into the atmosphere. However, in some parts of the world, people are dependent on cars, even while knowing the technology supporting them is unsustainable. In much the same way, wealthy white Southerners were dependent on slavery. In both cases, a backlash of denial set in. Climate change could lead to wars over dwindling resources, but like the Civil War, that is not inevitable.