Native Americans played a significant role in the formative years of the United States' history. During the mid-18th century, the Native Americans aligned themselves with the French settlers, who inhabited primarily the interior regions in America (West of the Appalachian Mountains) and who were far fewer in number. The French settlers had a reputation for treating the Native Americans with much more respect and dignity and included them as trading partners in their endeavors.

The bustling fur trade had led to prosperity for both the French and Native Americans, and they were content with their arrangement. Additionally, the French were not pressuring the Native Americans to leave their lands for any reason. Because of this respect and cooperative relationship, they joined together in an effort to drive the British colonists out of the Americas and reclaim their land.

Clearly, this endeavor was unsuccessful, and the Native Americans were pushed further back into the Frontier. Their involvement and animosity led to greater bitterness between the colonists and Native Americans, putting them at odds with one another in future conflicts and territorial disputes. In fact, their intervention at this early stage in the nation's history encouraged later movement Westward, in order to establish more colonies that would act as a barrier and dividing line to protect the East Coast from the Native Americans.

Native Americans played a major role in both the French and Indian War (also known as the Seven Years War) and the American Revolution.

During the French and Indian War, Native Americans allied themselves with the French in an effort to drive the British out of North America. Native Americans vastly preferred the French to the British because there far fewer French colonists than British colonists (John Wade speculates that the ratio was something like 20:1) and because the French treated the Native Americans much better than the British did. The French armed the Native Americans and were generous with the weapons they provided, which, in turn, made the Native Americans more dangerous to British colonists.

The colonists tried to keep Native Americans neutral during the Revolutionary War and were initially successful, but as the conflict grew larger, Native Americans realized that as much as they loathed British colonization, the United States as an independent country would be even worse. Almost all tribes allied themselves with the British in an effort to maintain what limited freedom they had under the Crown.

The Native Americans in the New World served as temporary allies with the British and French empires. Britain and France were able to take advantage of tribal animosities and cultivated relationships with some tribes while demonizing the others. For example, the British were allies with the Iroquois during the Seven Years' War, and the French were allied with the Huron—who also happened to be the Iroquois' biggest enemy.

Native American warriors attacked frontier settlements and helped to divert soldiers to defend the empire. Native Americans also attacked supply trains and assisted in scouting the territory. These European-Native relationships were matters of convenience, and the European armies only allied with the Native Americans when they were involved in a war. French traders and missionaries had long-term relationships with tribes, but ultimately the relationship between European and Native American proved to be one-sided in favor of the European power. In many circumstances the European power left the native tribe to fend for itself as soon as a European treaty had been concluded.

Agree completely with the post above, with a few additions.  These proxy wars took part mainly between the French and British, with the Spaniards sometimes involved.  The French had a distinct population disadvantage, having settled in the New World so late.  Only about 70,000 French settlers were here by 1754, compared with a million British-Americans.  This forced them to be both friendlier towards the Natives (so the French settlements and missions could continue to live here) and to ally with them when war came.  Natives knew the land, and how to fight guerrilla wars, and this gave the French an early military advantage.

The British also used Native allies where possible, usually with tribes that were enemies with the tribes allied with the French (confused yet?).  The end result being that after the French and Indian War, many Native tribes remained armed, and this intensified future resistance against the empires and later, the US.

There were other imperial conflicts in the New World at that time, but the French and Indian War is by far the largest and most significant.

In general, Native Americans were used as proxies in the wars of empire that were fought between the British and the French during the eighteenth century.

In these wars (like the Seven Years War, which is better known in the US as the French and Indian War), Native Americans fought on both sides of the war.  Typically, what would happen was that different Native American tribes would side with different imperial powers.  For example, if Tribe A took the French side, their enemies, Side B, would take the British side.  The Native Americans acted as scouts and as supplemental forces in these wars.