The Lithuanians made raids in Halych, Lodomeria, and Poland, almost reaching Cracow in November 1376. A riot broke out in Cracow against the unpopular queen mother, Elizabeth, on 6 December. The rioters slaughtered about 160 servants of the queen-mother, forcing her to flee to Hungary. Taking advantage of the situation, Władysław the White, Duke of Gniewkowo, who was a male member of the royal Piast dynasty, announced his claim to the Polish crown. However, Louis's partisans defeated the pretender, and Louis made him abbot of the Pannonhalma Archabbey in Hungary. Louis appointed Vladislaus II of Opole his governor in Poland.

In summer 1377, Louis invaded the territories held by the Lithuanian prince, George, in Lodomeria. His Polish troops soon captured Chełm, while Louis seized George's seat, Belz, after besieging it for seven weeks. He incorporated the occupied territories in Lodomeria, together with Galicia, into the Kingdom of Hungary. Three Lithuanian princes – Fedor, Prince of Ratno, and two princes of Podolia, Alexander and Boris – accepted Louis's suzerainty.