Final answer:
German and Italian aggression emerging from nationalistic fervor and fascist ideologies in the 19th and 20th centuries resulted in diplomatic tensions, alliance formations, and ultimately contributed to the outbreak of both World War I and World War II, significantly changing the political landscape of Europe.
Step-by-step explanation:
The aggression of both German and Italian forces significantly altered the political landscape of Europe. This aggression was rooted in the unification of Italy and Germany in the mid-19th century, propelling them as unified nation-states into the arena of European powers. The rise in nationalism, colonial ambitions, and military expansions led by Germany, coupled with Italy's own desires for greater power, disrupted the balance that had been maintained in Europe.
Following its unification, Germany became a dominant industrial, military, and political force, leading to tensions with neighboring countries, particularly France. The acquisition of Alsace-Lorraine by Germany from France after the Franco-Prussian War added to the animosity between the two nations. In response to these growing threats, countries throughout Europe began forging alliances to protect themselves and maintain peace; however, these alliances also meant that any conflict held the potential to devolve into a wider war.
The rise of fascism in the 1920s, both in Italy under Mussolini and eventually in Germany under Hitler, led to even more aggressive posturing in European and global politics. This culminated in World War II, beginning with Germany's invasion of Poland in 1939, and followed by its conquests across much of Europe. The world was once more plunged into a catastrophic war, reshaping the continent and the global order.