In practice, and geographically, Praga has always been set apart from Warsaw proper. Until 1791 the district was its own separate town and the inability to build a permanent bridge between Praga and Warsaw until the mid-18th century surely proved a factor in the separatism (ferries in the summer and a stroll across the iced-over Vistula in the winter were the main option for transit in the pre-bridge days). Finally in 1791 King Stanislaw August Poniatowski attached the district officially to Warsaw, dissolving it of its independence (at least on paper).
Praga wasn’t given much time to enjoy its new status as part of Warsaw thanks to the The Battle of Praga in 1794, which saw an aggressive invasion by the Russian army. Following the quick but devastating battle the Russians burned the entire district and massacred 20,000 Poles. During World War II Praga wasn’t quite as devastated as left-bank Warsaw (which isn’t really saying much if you’ve seen the condition Warsaw was left in). The Russians, again, arrived in Praga in July 1944 and stopped at the Vistula, famously leaving the Polish Home Army dangling during the Warsaw Uprising.
Today working-class Praga is a standard-bearer for cool, especially among those who find the tourist-heavy Old Town too Disneyfied and the sterile clubs of Warsaw proper as distasteful. Folks here prefer their bars dark and their fun improvised (most found on or near the district's main street, ul. Ząbkowska), and visitors can easily spend a day checking out the attractions, like street art murals, the illuminating Neon Museum, the Praga Koneser Center with its Polish Vodka Museum, learning about the history of the area by visiting the Praga District Museum or even seeing local streets with a pre-war vibe that were used as filming locations for Roman Polański's The Pianist.