Pre-revolution the individual colonies were already independent from each other having their own legislatures, governors, militias, etc. They all had loyalties to the crown of course and paid taxes to the British government, but they maintained a large level of autonomy.

During the war the problem that these independent entities were trying to make unified policy decisions without the structural ability to do so. The continental congress was too weak and unable to raise funds for the war effort. After the war, the founders realized that the loose confederation of states had shown weaknesses throughout the war and that change was needed. They needed a stronger centralized government to enact policy that benefited the whole of the collective states in a way only a unified government could. This is what lead to the constitutional convention and the federal government we more or less have today. Since it’s inception there has been constant debate over the power of states vs the federal government which contributed in large part to the Civil War.

TL;DR: More appropriate question would be, “how necessary was it for the individual states to create a strong centralized union as opposed to a loose confederation?”