Operation Storm begins in Croatia.
Operation Storm (Serbo-Croatian: Operacija Oluja / Операција Олуја) was the last major battle of the Croatian War of Independence and a major factor in the outcome of the Bosnian War. It was a decisive victory for the Croatian Army (HV), which attacked across a 630-kilometre (390 mi) front against the self-declared proto-state Republic of Serbian Krajina (RSK), and a strategic victory for the Army of the Republic of Bosnia and Herzegovina (ARBiH). The HV was supported by the Croatian special police advancing from the Velebit Mountain, and the ARBiH located in the Bihać pocket, in the Army of the Republic of Serbian Krajina's (ARSK) rear. The battle, launched to restore Croatian control of 10,400 square kilometres (4,000 square miles) of territory, representing 18.4% of the territory it claimed, and Bosnian control of Western Bosnia, was the largest European land battle since the Second World War. Operation Storm commenced at dawn on 4 August 1995 and was declared complete on the evening of 7 August, despite significant mopping-up operations against pockets of resistance lasting until 14 August.
Operation Storm was a strategic victory in the Bosnian War, effectively ending the siege of Bihać and placing the HV, Croatian Defence Council (HVO) and the ARBiH in a position to change the military balance of power in Bosnia and Herzegovina through the subsequent Operation Mistral 2. The operation built on HV and HVO advances made during Operation Summer '95, when strategic positions allowing the rapid capture of the RSK capital Knin were gained, and on the continued arming and training of the HV since the beginning of the Croatian War of Independence, when the RSK was created during the Serb Log Revolution and Yugoslav People's Army intervention. The operation itself followed an unsuccessful United Nations (UN) peacekeeping mission and diplomatic efforts to settle the conflict.
The HV's and ARBiH's strategic success was a result of a series of improvements to the armies themselves, and crucial breakthroughs made in the ARSK positions that were subsequently exploited by the HV and the ARBiH. The attack was not immediately successful at all points, but seizing key positions led to the collapse of the ARSK command structure and overall defensive capability. The HV capture of Bosansko Grahovo, just before the operation, and the special police's advance to Gračac, made it nearly impossible to defend Knin. In Lika, two guard brigades quickly cut the ARSK-held area which lacked tactical depth and mobile reserve forces, and they isolated pockets of resistance, positioned a mobile force for a decisive northward thrust into the Karlovac Corps area of responsibility (AOR), and pushed ARSK towards Banovina. The defeat of the ARSK at Glina and Petrinja, after a tough defensive, defeated the ARSK Banija Corps as well since its reserve was pinned down by the ARBiH. The RSK relied on the Republika Srpska and Yugoslav militaries as its strategic reserve, but they did not intervene in the battle. The United States also played a role in the operation by directing Croatia to a military consultancy firm, Military Professional Resources Incorporated (MPRI), that signed a Pentagon licensed contract to advise, train and provide intelligence to the Croatian army.
The HV and the special police suffered 174–211 killed or missing, while the ARSK had 560 soldiers killed. Four UN peacekeepers were also killed. The HV captured 4,000 prisoners of war. The number of Serb civilian deaths is disputed—Croatia claims that 214 were killed, while Serbian sources cite 1,192 civilians killed or missing. The Croatian population had been years prior subjected to ethnic cleansing in the areas held by ARSK by rebel Serb forces, with an estimated 170,000–250,000 expelled and hundreds killed. During and after the offensive, around 150,000–200,000 Serbs of the area formerly held by the ARSK had fled and a variety of crimes were committed against the remaining civilians there by Croatian forces. The International Criminal Tribunal for the Former Yugoslavia (ICTY) later tried three Croatian generals charged with war crimes and partaking in a joint criminal enterprise designed to force the Serb population out of Croatia, although all three were ultimately acquitted and the tribunal refuted charges of a criminal enterprise. The ICTY concluded that Operation Storm was not aimed at ethnic persecution, as civilians had not been deliberately targeted. The ICTY stated that Croatian Army and Special Police committed a large number of crimes against the Serb population after the artillery assault, but that the state and military leadership was not responsible for their creation and organizing. Croatia also adopted discriminatory measures to prevent the return of Serbs. Human Rights Watch reported that the vast majority of the abuses during the operation were committed by Croatian forces and that the abuses continued on a large scale for months afterward, which included executions of civilians and destruction of Serb property. In 2010, Serbia sued Croatia before the International Court of Justice (ICJ), claiming that the offensive constituted a genocide. In 2015, the court ruled that the offensive was not genocidal and affirmed the ICTY's previous findings.