As a percentage of the U.S. population, Maine gave the highest proportion of its residents to the Union Army (and in sheer numbers, to the Navy) of any Northern state. Discuss "why," factoring in authoritative pressures.
One of the reasons Maine was so zealous in support of its Northern cause can be seen in its geographic construction. Maine was the Northernmost state. This made it about as far removed from Southern slavery as possible. Maine was not a "border state" that played a strategic role. This meant that Maine, for the most part, did not have to deal with the divided body politic on the issue of slavery. In being the farthest from the South and the development of slavery, Maine was able to forcefully support the Union cause and not have to potentially worry about any political reprisals or uprisings among its population. Thus Maine was able to tout itself as a clear advocate of the Northern Cause. President Lincoln's first Vice President was Hannibal Hamlin, himself a supporter of rights for people of color. This was another example of how those in positions of authority were able to clearly voice support for the Northern cause without reticence.
To a great extent, Maine's history could also be seen as a part of its Northern support. Maine was admitted to the nation as a "Free state" in the Compromise of 1820. From this instant, Maine always identified itself as positioned against slavery. This helped to galvanize Maine into a force that could willingly give to the Union cause, helping to show how history can be an authoritative force. It is not entirely surprising to see this as part of the reason Harriet Beecher Stowe wrote her anti-slavery opus Uncle Tom's Cabin in Brunswick, Maine. The spirit of abolitionism so prevalent in the novel was part of the Maine culture that fed Stowe's mind and heart. This shows how culture was an authoritative force in establishing Union support. These examples help to show why Maine military support was so dominant for the Union cause at a time when the issue was so thorny and potentially divisive.