No enough information to answer, you either need to put the question in a historical context or within a time frame
Adolph Hitler - the Nazi dictator of Germany - invaded Poland on September 1, 1939 Britain and France declared war on Germany for this unprovoked act of aggression
The Soviet Union.
The first attack, or act of hostility; the first act of injury, or first act leading to a war or a controversy; unprovoked attack; assault; as, a war of aggression. "Aggressions of power."
The Soviet Union and Germany had non-aggression pact called the Molotov-Ribbentrop pact.
His acts of aggression included mainly the invading of other countries and the killing of millions of innocent people.
Germany committed many acts of aggression in WW2, mainly in invading and occupying most of the free countries of Europe, and indiscriminately bombing Britain.
Japan's first act of open aggression happened on 1871. Okinawa was being claimed by China, which caused Japan to attack Taiwan.
The first act of aggression by the German Nazis on an innocent country was the blitzkrieg attack on Poland in September of 1939. This sparked World War 2 and launched Hitler's campaign to gain all the European nations.
The first act of aggression in World War I itself was when the Austro-Hungarian empire sent artillery into Serbia in preparation for an invasion. The act that triggered this was the assassination of Archduke Franz Ferdinand.
The invasion of Etheopia.
It was the other way around. Germany invaded Belgium in World War I as the first act of aggression. Germany invaded Belgium as a way to circumvent French defenses along the German border (the Maginot Line).
That Germany will get the western part of Poland (Russian territory), Russia will get the Eastern half and Germany promises not to invade Russia.