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Political assassination was frequent in highly civilized 8th century Spain. Most murders were committed by rival factions. So, too, in the Ottoman Empire, where assassination was used for political consolidation and transfer of power. When Sultan Murad III died in 1595 leaving 20 sons out of 47 surviving children, Murad's successor, Mohammed III, eliminated his competition by murdering his 19 brothers.
European rulers rarely resorted to assassination abroad, partly because of a sense of fair play inherited from the medieval chivalric code, partly because assassinating rival monarchs inevitably invited retaliation. In the Italian city states of the Renaissance, of course, the Medicis, Viscontis and Sforzas practiced murder against rivals in politics, love or family quarrels with satanic ardor. The first and possibly the worst was Ezzel-ino da Romano, the 13th century despot of Padua and Verona. "Here for the first time," wrote Historian Jacob Burckhardt, "the attempt was openly made to found a throne by wholesale murder and endless barbarities." Pope Alexander VI (Rodrigo Borgia), with his children Cesare and Lucrezia, used assassination for political ends when they eliminated the son of the King of Naples in the 16th century.
As part of a church-state struggle, four knights assassinated Thomas a Becket, the Archbishop of Canterbury, in 1170, believing (with some reason) that Henry II wanted his former friend eliminated. The Reformation brought with it assassination as an instrument of religion, if not foreign policy, especially in the struggle between Roman Catholics and Huguenots in France. Before his accession to the throne, Henry III helped his mother, Catherine de Medicis, plot the assassination of Admiral Coligny and other Huguenot leaders. He himself was assassinated in 1589 by a monk; his successor, Henry of Navarre, a Huguenot who later became a Catholic, was murdered in 1640 by a Catholic religious fanatic.
Elizabeth I of England survived a number of plots on her life, including some morally backed, if not specifically commissioned by the Vatican and Philip II of Spain. But the English monarchs themselves tended to rely on executions under law rather than assassinations. Mary, Queen of Scots, Thomas More and others were thus dispatched.
The seismic collapse of Europe in 1914 brought on the modern age of political assassinations. Russia's Prime Minister Pyotr Stolypin had already been killed in 1911 by Dimitri Bogrov, who may have been acting as a revolutionary or a police agent. Then Serbian nationalists assassinated Austrian Archduke Franz Ferdinand—a dissident act that brought on the first World War.
Stalin murdered millions, but seldom assassinated to enforce foreign policy. It might be argued that the elimination of Leon Trotsky in his Mexican exile in 1940 was an act of policy, but he was a Russian. A better example was the death of Czechoslovak Foreign Minister Jan Masaryk in 1948, a defenestration that the official report described as suicide but was almost surely an act of the Kremlin.