At that time, the Americans undertook a ruthless fight for independence, achieving their first successes against the British. Without hesitation, in 1776, he decided to emigrate to America. There, his education and leadership skills were immediately recognized. He was appointed an engineer in the U.S. Army and ordered to fortify a city near the Delaware River. His true fame and recognition came with the construction of fortifications near Saratoga, which secured the Americans victory, and later with the construction of the West Point fortress on the Houston River. These successes earned him a promotion to the rank of brigadier general, and West Point became the home of the U.S. Military Academy. Numerous monuments to the hero stand in American memory, including those in La Fayette Park in Washington, D.C., on the Saratoga Battlefield, in Chicago, and Boston.

Tadeusz Kościuszko was, above all, a Pole. Despite the difficult situation in Poland, he returned to Poland. The Four-Year Sejm passed a resolution organizing a 100,000-strong army. Kościuszko was commissioned and promoted to major general of the Polish army. In 1791, the May Constitution was passed, overthrowing the old order and abolishing the pernicious privileges of the nobility. The Targowica Confederation opposed this constitution, bringing a massive Russian army into Poland. The Poles, with a small force, resisted. Kościuszko distinguished himself at the Battles of Zielenice and Dubienka. He was one of the first to receive the Virtuti Militari Cross. However, the war was lost, resulting in the Second Partition of Poland in 1793.

Those who refused to accept this fact were forced to emigrate, primarily to Saxony. Defeat in the war with Russia and the Second Partition of Poland shocked Polish society and created a favorable climate for an armed struggle for the country's independence. A conspiracy center, led by Ignacy Potocki and Hugo Kołłątaj, arose in Dresden. Tadeusz Kościuszko was appointed commander-in-chief of the insurrection. He sought French aid but failed to receive it. He decided that Poles could only rely on themselves. He drew on the American experience and wanted to involve the entire nation, including the peasants, in the fight. After taking the oath in Kraków in March 1794, he immediately joined the fight, winning his first magnificent victory at Racławice, where the peasants proved they could "sustain and defend the Motherland." Things then became increasingly dangerous. The Prussians entered the war, and new forces arrived from Russia.