With the events leading up to the "shot heard 'round the world" at Lexington, MA in April of 1775, the British-American colonies opted for independence from their mother-country. With a handful of victories and a basketful of defeats, the Continental Army outlasted Great Britain.
You may have Patriot ancestors or Loyalist ancestors or both. Your ancestors may have switched sides at some point between 1775 and 1783.
The best example of switching sides was Brig. Gen. Benedict Arnold. He was one of Washington's most prized generals. Vanity, greed, politics and other factors led Arnold to agree to sell the plans to West Point to the British. The plan failed and Arnold went from hero of Saratoga to traitor.
Some Hessian soldiers [German mercenaries] deserted and enlisted in the Continental Army. Other soldiers deserted and switched sides as well.
Loyalists were known to switch sides as well. After the war most of the Loyalists fled to Canada or returned to England.
The pension files will only help if you have ancestors who served in Continental Line [regular] regiments. Militia companies were frequently attached to Line units for a brief time and qualified those militia men for pensions. Check state archives for military records for soldiers. Some are online. Check the DAR and SAR websites to search for soldiers. Also check for other lineage organizations that focused on Rev War soldiers and sailors.
For militia service, biographical collections, local and state records are your best options.
Loyalist records? Search for websites that focus on Loyalists. There are a few of them out there.
As always, check Ancestry, Family Search and other sites to see what military records they have.