By the spring of 1919 the situation in the borderlands was a tangle no map could quite represent. The German Empire had collapsed; the Russian Empire had collapsed; in their place a half-formed Polish republic, a half-formed Soviet republic, a contested Lithuanian state, a brief Belarusian National Republic, and German occupation troops who had not yet gone home were all in motion across the same forests and railway lines. Pilsudski had to choose: continue the Polish-Ukrainian War in Galicia or pivot north and face the Bolsheviks. He chose north. As the official histories tactfully put it, his decision was based partly on strategy - and partly on the fact that he had been born in Vilnius and would not see it under Soviet rule. By early April the Polish line ran along the Yaselda River and the Oginski Canal. Bolshevik forces held Vilnius, Lida, Baranavichy, and Lunynets. The Germans held Grodno. Lasocki was sent to take Lida.

At five in the morning on 16 April 1919, Polish forces attacked Lida from the north, west, and south simultaneously. The plan was to overwhelm the small Bolshevik garrison quickly. The plan did not survive contact with the Bolshevik garrison. Defenders dug in around the railway station, joined by some of the Jewish residents who had armed themselves, and they refused to break. Pilsudski had predicted the town would fall in hours; instead, it took most of two days. Reinforcements were sent forward by train as the fighting dragged on - the Second Battalion of the 5th Legions Infantry under Captain Bernard Mond, the First Battalion of the 6th Legions under Major Stefan Dab-Biernacki. Both men would have long careers in the interwar Polish army, and both would face very different fates after 1939.

The Bolshevik defenders summoned an armored train, which rolled out of the station and pinned the Polish advance for hours with its guns. Polish soldiers crossed the rail tracks anyway and pushed into the suburbs, fighting from one wooden house to the next through the night of 16-17 April. By dawn they had brought up enough hand grenades to blow the rails behind the train, cutting off its retreat. At four in the morning on 17 April, Lasocki ordered the general assault, focused on the station. After an hour the town was in Polish hands. The Poles captured the armored train, weapons, ammunition, and 350 prisoners of war. Bolshevik forces retreated east, chased by Polish cavalry of the 7th Lublin Uhlan Regiment under Major Janusz Gluchowski. Polish engineers were already at work on the rails. By noon Pilsudski himself had arrived in Lida.

Casualty figures for Lida are vague - several killed and wounded on each side, in the dry phrasing of the staff reports - but for an action of its size the proportion of dead was significant, and for the families involved the numbers did not need to be large. The day after Lida fell, the trains were running again toward Vilnius. The Polish offensive Pilsudski had been planning swept into the city on 19 April. The whole eastern reach of the new Polish Republic now ran through Lida's railway station. The Tomb of the Unknown Soldier in Warsaw bears the inscription "LIDA 16 IV 1918 - 28 IX 1920" - the dates spanning the start of independence operations and the end of the Polish-Soviet War. The town itself sits today in western Belarus, its old market square still recognizable, its station rebuilt after the still-greater catastrophes of 1939, 1941, and 1944.