Editing 1621 (section)

=== October&ndash;December ===
* [[October 9]] &ndash; The [[Treaty of Khotyn]] is signed between the [[Ottoman Empire]] and the [[Polish–Lithuanian Commonwealth]], ending the [[Polish–Ottoman War (1620–21)|First Polish-Ottoman War]].<ref name="Żółkiewski1959"/>
* [[October 9]] (September 29 O.S.) &ndash; The [[Pilgrim Fathers|Pilgrims]] of [[Plymouth Colony]] and [[Wampanoag people|Wampanoag]]s celebrate a harvest feast (three days), later regarded as the ''[[Thanksgiving (United States)|First Thanksgiving]]'', noted for the temporary peace between the English and the local Indians. The celebration is believed by later historians to have coincided with [[Michaelmas]], observed on September 29 by the Anglican Communion on the calendar used in England at the time. 
* [[November 11]] &ndash; The ship ''[[Fortune (Plymouth Colony ship)|Fortune]]'' arrives at [[Plymouth Colony]], with 35 more settlers.
* [[December 31]] &ndash; [[Thirty Years' War]]: The [[Peace of Nikolsburg]] is signed between [[Ferdinand II, Holy Roman Emperor]] and [[Gabor Bethlen]], Prince of Transylvania. Bethlen agrees to renounce his claims to Hungary. In return Bethlen receives several counties and lands along the eastern border of the Holy Roman Empire, and Moravia is granted religious freedom.
* [[December]] &ndash; The Dutch mathematician and astronomer, [[Willebrord Snel van Royen]] (1580–1626), reveals he has rediscovered the [[law of refraction]], also known as ''Snellius' law''.<ref name="Sarton1936">{{cite book|author=George Sarton|title=A Volume of Studies on the History of Mathematics and the History of Science: Presented to Professor David Eugene Smith on His 76th Birthday (Jan. 21, 1936)|url=https://books.google.com/books?id=ddPuAAAAMAAJ|year=1936|publisher=Saint Catherine Press Limited|pages=724–725}}</ref>