Teri-- I hope to provide you with a short answer to a rather complex question.
The Black Hawk War eruped over the essential incompatability between two cultures and their goals. Persons looking for the initial cause of the war must look earlier than 1832. Many historians point to the disputed Treaty of 1804, where the Sauk and Fox tribes (essentially co-existing in the Rock Island area of Illinois) were informed that their lands had been ceded for a pittance to the U. S. by an agreement signed by a native delegation led by Quashquame. The Sauk and Fox were allowed to live on the land until it was sold, which didn't happen until the so-called "Lead Rush" of the 1820s. Also, the Sauk allied themselves with the British during the War of 1812, and war-parties under Black Hawk won victories and committed depredations on Americans. This did not endear the tribe or BH to the local American population. As previously mentioned the issues are complex!
During the War of 1812, BH's leadership among the Sauk was usurped by a younger man named Keokuk. Keokuk emerged as a spokesman and negotiator for the Sauk... and the Americans encouraged his participation in councils and treaty-making.
By 1831, the surge of American emigration into north-western Illinois and southwestern Michigan Territory (today's Wisconsin)had prompted the land sales stipulated by the Treaty of 1804. The Sauk and Fox were forced to remove across the Mississippi, leaving their villages, ancestral lands, and cornfields still planted with corn behind.Keokuk urged a peaceful removal, but BH lead a contingent of Sauk and Fox upset with the removal back across the river into Illinois. BH's retrun across the Mississippi promted the raising of the militias in both Illinois and the M. T. BH backed down, and signed a treaty (known later as the "Corn Treaty") whereby he formally recognized the validity of the Treaty of 1804, and the requirements of native removal after land sale. He then revoved across the mIssissippi into present-day Iowa.
But the winter in Iowa 1831-2 was a hard one and the food ran out in the Sauk and Fox camps. Murmurs turned to an uproar, and a segment of the Sauk and Fox appealed to BH to again return across the Mississippi to their former homes and corn fields. Likewise, advisors like Na-pope (the number one civil chief of BH followers known as the "British Band") and White Cloud, the Winnebago Prophet, urged the movement based on assurances of support from the British and a rising of other native tribes that would form alliances with the British Band.
On April 5, 1832, BH disregarded the treaty he signed the previous year, and led a party of some 450 well-armed, mounted warriors and their families, (about 1,000 souls all together...about 17% of the estimated Sauk and Fox population at that time) plus about 10 lodges of the Kickapoo across the Mississippi into Illinois. Gov. John Reyniolds immediately appealed to the U. S. Army for help and called up his state's militia. SOme historians have incorrectly characterized this as a "political move" on the part of Reynolds. In fact, this was the thrid time the militia had been called up to deal with an Indian threat in the last five years.
Attempts were made to induce BH to return across the river peacably. On April 23, Henry Gratiot, a U. S. Indian sub-Agent and a delegation of Winnebago tribal leaders tried to meet with BH at White Cloud's Village... Prophet's Town. There, Gratiot was essentially kept a prisoner oin a lodge, and his white flag pulled down, and a British ensign raised. Gratiot delivered the message of General Henry Atkinson, essentially demanding BH's return to Iowa. BH steadfastly refused... and Gratiot was later forced to canoe for his life for Fort Armstrong, pursued by BH's young men in canoes. A wide-eyed and exhausted Gratiot reported that in his opinion, no peaceful settlement with BH was now possible.
Unfortunately, the promise of native tribes rising up never materialized. Tribes like the Potowatomie and Winnebago were sympathetic, but refused to "formally" ally with BH for fear of American retaliation. In fact, BH was in the midst of a dog feast and further talks with Potowatomie tribal leaders on May 14, when the presence of a militia battalion was reported just a few miles away at Old Man Creek (present-day Stillman Valley, IL.) Na-pope sent three men with a white flag to call a parley with the Americans, while BH sent five warriors to a ridgetop to watch the proceedings.
Things went bad from the start. The three Sauk with the white flag were brought to the militia camp, but the Sauk spoke no English, and the militiamen spoke no Sauk. Then the militia spotted the warriors on the ridgeline, and immediately suspected a trick. One American turned and shot and killed one of the Sauk parely party in cold blood. The other two Sauk eventually got away. In the meantime militiamen (some charged up with whiskey) took off on horses after the five warriors on the ridgetop. Fighting ensues, and the warriors took off to report the developments to BH.
BH, incensed, scraped together forty mounted warriors and charged at the Americans---an attack BH later wrote he thought would be his last. In the gathering darkness, militia resistance crumpled, then collapsed. In an unreasoned and panic-filled route, the militia (save a breif stand on a small knoll where the present-day monument stands)fled from the field. Twelve militiamen were killed and later mangled. But the reports the flooded the region spoke of hundreds of casualties at the hands of thousands of blood-thirsty Indians.
Panic swept the land... and Black Hawk's War was on!