In the annals of war, victory often does not go to the largest military force. The fight for independence with Great Britain is one example in history of the accuracy of this statement.
Although the British were considered the best fighting military in the world, the American colonies represented some unique challenges that worked in the favor of the revolutionaries. The British had a superior and commanding naval force that could substantially block imports and export from the colonies' port cities. Fortunately for the Americans, the main battles were fought on land, where the British army was significantly smaller and more evenly matched with American militias. At one point during the war, the British were so undermanned they hired German mercenaries.
Having a home-field advantage favored the Americans. The British believed, based on their European experiences, they could manage the war from Great Britain. It would often take several weeks for orders, men, and supplies to arrive, crippling the British supply lines and limiting how quickly the British could engage in battle. The Americans used their superior knowledge of the country's geography to their advantage, frequently picking battlefields favoring smaller, more agile troops.
One tactic the Americans used that absolutely infuriated the British were guerilla warfare tactics, hiding and then ambushing the British troops! In Europe, the Europeans had specific rules of war and combat rules for engagement. Not fighting on an open battlefield was highly offensive to the British military. The British had seldom encountered an enemy that did not respect combat rules.
One example is that under the general rules of combat, military officers were not supposed to be targeted by the opposing side. The Americans, without hesitation, took direct aim at the British officers, who were easy to identify as they generally sat on horses above the fray. Another rule the Americans did not adhere was the British had battle hours when the battle could begin and when the war ended during the day. Americans attacked at all hours of the day or night. The unconventional style of fighting was a problem for a military anchored by tradition and conventional tactics.
Public opinion in the colonies and Britain was split. The British Parliament had a difficult time justifying and paying for a war an ocean away. Even the Loyalists in the colonies questioned the wisdom of fighting against people with familial ties to Britain and generationally related. Many historians believe the British military and leadership, having made their residence in America, were reluctant combatants. Their reluctance manifested in poor tactical decisions leading to several defeats that only encouraged more Americans to enjoin the battle.
If these factors were different, would the outcome had been the same? Historians generally are not favorable to "what ifs," (speculation) and given the rapid decline of the European powers (Britain and France), it would be hard to imagine the British sustaining their colonial hold on the colonies for much longer. The main factors of globalization and decline of the British Empire probably escalated the American drive to independence as much as the political climate in America.