This is such an interesting way to phrase this question about Maine becoming a state! Yes, I suppose it WAS a long "trip" for Maine to become a state; however, please realize that the United States of America has 50 states, and Maine is considered the "23rd state," and made so in 1820. But, yes, considering Maine is one of those states on the East Coast and was originally part of the Massachusetts Bay Colony, it was kind of late in coming. Let's consider the "three most significant factors" as to why. I'll put them in chronological order instead of order of importance.
1. Native Opposition (and Confusion due to a confusing treaty): The Native Americans (specifically of the Abenaki Tribe) fought quite valiantly against the English colonists for more than one hundred years. The Abenaki killed, held hostages, and held others for ransom. As a result, it wasn't the easiest territory to settle. Adding to this issue was the unclear language of the treaty that ended the revolution which failed to define Maine's borders clearly. As a result, Maine was still considered part of Massachusetts.
2. The War of 1812: Even after the American Revolution, the British were still fighting for control over Maine during the War of 1812. In fact, England occupied the eastern part of Maine (that is, near its eastern coast) during the conflict. Even after the war was over, the northern boundary (that is, the boundary between America and British North America) was still in dispute). Further, that boundary wasn't confirmed until 1842, actually AFTER Maine became a state!
3. Irony of Massacusetts Bay Unity: What is interesting in Maine's state history is that even though it was originally part of the Masachusetts Bay Colony (the first in the nation), that is the same reason why it took so long for Maine to actually become its own state. The topography of Maine always made it seem separate from Massachusetts, so the settlers tried to secede from Massachusetts. The first vote failed, but the second one (after the war of 1812) stuck. It stuck the second time because royalists refused to defend Maine from the British. Therefore, the state of Maine (the 23rd state of the USA) was formed on March 15, 1820 and is actually considered a part of the Missouri Compromise.
In 1820 Maine voted to secede from Massachusetts. The secession and formation of the state of Maine as the 23rd state occurred on March 15, 1820 as part of the Missouri Compromise, which geographically limited the spread of slavery and enabled the admission to statehood of Missouri the following year, keeping a balance between slave and free states.