The new Congressional and Executive branches authorized a standing army composed of professional soldiers rather than relying on state militias.

[1] The Legion was primarily formed in reaction to multiple defeats in the Ohio country in 1790 and 1791 and to assert U.S. sovereignty over U.S. borders in the western territories and Great Lakes regions.

[2]: 10  By 1785, however, a cash-strapped Congress authorized 700 recruits to form the First American Regiment, which served in the Western territories, both to expel illegal settlers and to protect those who had purchased their lands from the United States.

His initial force was roughly the same size as Harmar's, so Congress authorized a second infantry regiment of 2,000 soldiers, but only for six months.

[2]: 27  President George Washington drafted a list of sixteen general officers from the American Revolutionary War to lead an expanded Army in the Northwest, including Benjamin Lincoln, Daniel Morgan, and Friedrich Wilhelm von Steuben.

After consulting with his cabinet, he picked Anthony Wayne to lead the new professional army, although Washington initially considered him too vain.

[3]: 205  Influenced by treatises from both Henry Bouquet and General Friedrich Wilhelm von Steuben,[4] and at the recommendation of Secretary of War Henry Knox and General von Steuben,[2]: 27  it was decided to recruit and train a "Legion", a force that would combine all land combat arms of the day (cavalry, heavy and light infantry, artillery) into one efficient brigade-sized force divisible into stand-alone combined arms teams.

Congress agreed with this proposal to augment the small standing army until "the United States shall be at peace with the Indian tribes."

They were trained to fire a paper cartridge consisting of "one ball and three heavy buckshot," and to aim at the waistband to maximize lethality.

By contrast, regular infantry were trained to form in open order and merely point their weapons towards their enemies to maneuver and fire more quickly.

[12]: 63  Wayne requested copies of General von Steuben's Regulations for the Order and Discipline of the Troops of the United States, which was out of print; he complained that officers from the Revolution were "rather rusty.

When the squadron was ordered north to Fort Greenville, some troopers did not have boots, having had to relinquish them to infantry soldiers who had previously departed.

[12]: 209  They were superseded by a new detachment of 90 scouts and spies organized into three companies[13]: 25  under the command of Captain William Wells,[12]: 209  a son-in-law of Miami war chief Little Turtle who unexpectedly joined the Legion.

[13]: 25 [12]: 64 The Legion created the first training camp used by the United States Military, at Legionville in western Pennsylvania, on the banks of the Ohio River.

As Wayne prepared to advance in 1794, Knox ordered him on 31 March to build and man a fortification on the site of Fort Massac.

This was to prevent any action against Spain by the French Revolutionary Legion, a force under George Rogers Clark that was recruiting at the same time.

This chain of frontier forts eventually reached far north towards Lake Erie and closely resembles the modern border of Ohio and Indiana.

The Legion of the United States was engaged in several attacks on their convoys as the expedition pushed further into Native American strongholds, chiefly towards the Maumee Rapids.

[14] Anticipating war, the British constructed Fort Miami south of Lake Erie in the spring of 1794 and garrisoned it with 120 infantrymen and a detachment of 8 cannon.

[3]: 262 On 30 June 1794, just outside the gates of Fort Recovery, built on St. Clair's battlefield, a pack-horse convoy led by Major William Friend McMahon was attacked by 2,000 Native Americans.

After Major McMahon was killed and the rest of the survivors fled to the protection within the fort, a full-scale attack was made on the fortification.

The most notable engagement in which the Legion participated was the Battle of Fallen Timbers, southwest of present-day Toledo, Ohio, on 20 August 1794.

By the time the Legion reached this area, it had less than half its authorized numbers, with many soldiers defending the supply trains and forts.

[13]: 23, 28 The Legion conducted a movement to contact and found an established ambush in a field of trees that had blown over in a storm (the "fallen timbers").

Although the battle lasted little more than an hour, Fallen Timbers was the culmination of an arduous campaign and owed its success to the intense training and discipline of the Legion of the United States.

That September, he led the Legion from Fort Defiance and marched unopposed for two days to the Kekionga, the Native American city where Harmar had been defeated four years earlier.

[7]: 139  After Wayne's death at Fort Presque Isle on 15 December 1796, his second-in-command, Wilkinson (later found to be a spy for the Spanish government),[16] became the Senior Officer of the Army.

"[22] This alludes to the crest of the 3rd Infantry Regiment's coat of arms, which shows a black cocked hat with white plume.