The Catholic League’s two armies have united…

Mohammadreza Isfahani builds the Naghsh-i Jahan Square (Persian: "Image of the World Square") in Isfahan.

Bacon writes Novum Organum (”the New Organon”) in 1620.

The second part of his planned magnum opus, Bacon intends for this work to replace Aristotle’s Organon, for whom he reserves particular criticism.

The Bohemians have reneged on their offer of their crown, but the Transylvanians continue to make surprising progress, succeeding in driving the Emperor's armies from this country by 1620.

Although Bethlen has conquered most of Royal Hungary, he is not averse to a peace, nor to a preliminary suspension of hostilities, and negotiations had been opened at the conquered towns of Pozsony, Kassa and Besztercebánya.

They had initially led to nothing because Bethlen had insisted on including the Czechs in the peace, but finally a truce is concluded on February 4, 1620, under which Bethlen receives thirteen counties in the east of Royal Hungary.

The Spanish send an army from Brussels under Ambrogio Spinola to support the Emperor.

In addition, Oñate, the Spanish ambassador to Vienna, persuades Protestant Saxony to intervene against Bohemia in exchange for control over Lusatia.

The Saxons invade, and the Spanish army in the west prevents the Protestant Union's forces from assisting.

Oñate conspires to transfer the electoral title from the Palatinate to the Duke of Bavaria in exchange for his support and that of the Catholic League.

The Protestant Union, facing the superiority of the League army of thirty thousand men confronting the Union's army of ten thousand, agrees on July 3, 1620, under the terms of the Treaty of Ulm, to cease all hostilities between both parties during the war in Austria and Bohemia and cease its support of Frederick V.

Without the risk of an attack, the League can use all its military forces to support the emperor.

The army is in the same month relocated to Upper Austria.

The Diet at Besztercebánya elects Bethlen king of Hungary on August 20, 1620, after the collapse of negotiations between Bethlen and Ferdinand.

Realizing, however, that Hungary's Roman Catholic nobles will never accept a Protestant king, he refuses to be crowned.

War breaks out at this point between Bethlen and Ferdinand.

A battle in Les Ponts-de-Cé in August 1620 definitively ends the civil war waged by Marie de Médicis against her son.

This short rebellion, subdued easily by the King's troops, is known in France under the name of "Drôlerie des Ponts-de-Cé" ("The Joke of Les Ponts-de-Cé").

Poland has since 1614 encouraged rebellions in the Ottoman vassal principalities of Moldavia and Wallachia, its Ukrainian Cossacks having skirmished with the Ottoman Empire’s Crimean Tatars, and Poland’s King Sigismund III Vasa having stealthily supported the Habsburgs.

General Stanislaus Zolkiewski—who, despite his advanced age (he is over seventy), has continued his active service as a military commander—advances with some ten thousand Polish troops into Moldavia and on September 20, 1620, joined by some Cossacks and Moldavians, defeats a superior Turkish-Tatar army at the battle of Jassy (Iasi).

Courthope, after losing his two ships to mutiny and sinking by the Dutch, had fortified the island by erecting forts to overlook approaches from the east.

With thirty-nine men, he has held off a Dutch siege for one thousand five hundred and forty days.

Shot in the back by the Dutch in October 1620 while rowing back to Run in a small boat, and refusing to surrender, he leaps into the sea and swims for it, dying en route.

The English and their local allies depart without a struggle.

The Catholic League's army (which includes in its ranks René Descartes ), under Tilly’s command, pacifies Upper Austria while ...