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How did the Union of Krewo connect Poland and Lithuania before the Union of Lublin?

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Map showing Poland's territory in 1634 under the reign of Wladyslaw IV Vasa, shaded in pink and spanning from the Baltic Sea in the north to near Kyiv in the southeast. Major present-day cities such as Warsaw, Krakow, Gdansk, Vilnius, Minsk, Lwow (Lviv), Pinsk, and Kyiv are marked within the territory, with surrounding cities like Moscow, Riga, Vienna, and Budapest shown for reference. — Polish-Lithuanian Commonwealth Poland's territory in 1634, during the reign of Władysław IV Vasa.

The Union of Krewo, concluded on August 14, 1385, established a personal union between Poland and Lithuania by linking the two realms under a single sovereign. This agreement was initiated when the Lithuanian Grand Duke Jogaila agreed to marry the Polish Queen Jadwiga, convert himself and his pagan subjects to Roman Catholicism, and assume the Polish throne as King Władysław II Jagiełło.1234

Before the Union of Lublin in 1569, this connection functioned primarily as a loose alliance held together by a common ruler. While the two states remained distinct—each retaining its own administration, laws, and armed forces—the union facilitated significant cultural and political integration. Over time, the Lithuanian nobility increasingly adopted Polish language, culture, and political structures, such as the establishment of a Sejm (parliament) modeled after the Polish system. This period of personal union also allowed the two nations to coordinate militarily, most notably in their decisive victory against the Teutonic Order at the Battle of Grunwald in 1410.1235