June 15 is the date when, in 1775, Russian troops under the orders of Catherine II destroyed the Zaporizhian Sich.
Zaporizhian Cossacks were considered the defenders of the border, beyond which the Ottoman Empire began, so Moscow was generous with privileges, funding, and exemptions from various duties. This state of affairs lasted for over a century, but with the rise of Catherine II to power, the situation began to change rapidly.
Catherine began to actively strengthen the vertical of power and pacify the rebellious. The Zaporizhian Sich was considered a "hotbed of freedom and free thought," so its liquidation became a matter of time.
In 1764, the institution of the hetmanate was abolished, and almost a year later, the right to local self-government was taken away from the lands of Slobozhanshchyna. However, Catherine still needed the Sich, so she was in no hurry to destroy it. The Cossacks were needed by the empress for war.
The Zaporizhians helped Moscow achieve victory in the Russo-Turkish War of 1768-1774. Returning from the Ottoman campaign, Russian troops led by Peter Tekeli (a total of over 100,000 men) treacherously and without any warning attacked the Zaporizhian Sich. This came as a complete surprise to the Cossacks, a significant portion of whom had not yet returned from the war or were engaged in fishing. The Sich was guarded by a garrison of 3,000 men.
A hastily convened council by the Cossack hetman Peter Kalnyshensky decided to refrain from bloodshed and lay down their arms. Although the rank-and-file Cossacks were inclined to resist.
On June 15, Russian troops completely destroyed the Sich, transporting all property and documents to St. Petersburg. The leadership was accused of treason and sentenced to hard labor. The Cossack judge Pavlo Holovaty and military scribe Ivan Hloba were exiled to Siberia, while the 85-year-old Cossack hetman Peter Kalnyshensky was imprisoned in the Solovetsky Monastery.
In a manifesto dated August 14, 1775, Catherine II announced the liquidation of the "den of drunkards and ruffians" who lived in ignorance, "with the extermination in the future of the very name of the Zaporizhian Cossacks." And further: "…there is no longer a Zaporizhian Sich in its political monstrosity." In the best traditions of demagoguery, the "enlightened" empress presented the destruction of the Sich as the fulfillment of a monarchical duty before God, before the empire, and even "before humanity as a whole."
On the annexed lands, huge estates were granted to the favorites and close associates of Catherine II. At that time, intensive colonization of "New Russia" began, as the steppe region of the Black Sea became known.