The Kassa attack was the June 26, 1941 aerial bombing

Airstrike

An air strike is an attack on a specific objective by military aircraft during an offensive mission. Air strikes are commonly delivered from aircraft such as fighters, bombers, ground attack aircraft, attack helicopters, and others...

 of the city

City

A city is a relatively large and permanent settlement. Although there is no agreement on how a city is distinguished from a town within general English language meanings, many cities have a particular administrative, legal, or historical status based on local law.For example, in the U.S...

 of Kassa

Košice

Košice is a city in eastern Slovakia. It is situated on the river Hornád at the eastern reaches of the Slovak Ore Mountains, near the border with Hungary...

, today Košice (Slovakia

Slovakia

The Slovak Republic is a landlocked state in Central Europe. It has a population of over five million and an area of about . Slovakia is bordered by the Czech Republic and Austria to the west, Poland to the north, Ukraine to the east and Hungary to the south...

), then a part of Hungary. This attack became the pretext for the government of Hungary to declare war

Declaration of war

A declaration of war is a formal act by which one nation goes to war against another. The declaration is a performative speech act by an authorized party of a national government in order to create a state of war between two or more states.The legality of who is competent to declare war varies...

 on the Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

, on 27 June 1941.

On June 26, 1941, four days after Germany

Nazi Germany

Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...

 attacked the Soviet Union in violation of the Molotov-Ribbentrop non-aggression treaty

Molotov-Ribbentrop Pact

The Molotov–Ribbentrop Pact, named after the Soviet foreign minister Vyacheslav Molotov and the German foreign minister Joachim von Ribbentrop, was an agreement officially titled the Treaty of Non-Aggression between Germany and the Soviet Union and signed in Moscow in the late hours of 23 August 1939...

, three unidentified planes of apparently Soviet origin bombed the city, killing and wounding over a dozen people and causing minor material damage.

The true identity of the attacking nation has never been established. The official explanation preferred by Soviet historians was the idea of a feigned attack by Germany to provoke Hungary into attacking the Soviet Union, employing Soviet planes captured on conquered airfields. Another possibility is that the Soviet bomber

Bomber

A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...

s mistook Kassa for a nearby city in the First Slovak Republic, which was already at war with the Soviet Union.

After the incident Hungary declared itself at war with the Soviet Union.

Source

• "New Twist to an Old Riddle: The Bombing of Kassa (Košice), June 26, 1941," Journal of Modern History, Vol. 44, No. 2, (June 1972), pp. 232–42.