I don't disagree with Buchanan's main argument - that the goal of the Mumbai terrorists was to provoke a war between India and Pakistan - as much as his callous characterization of Princip, and putting him in the same category as the Mumbai attackers and the 9/11 jihadists.
Was Princip really a terrorist? Take just this common-sense definition of terrorism from Wikipedia:
Most common definitions of terrorism include only those acts which are intended to create fear (terror), are perpetrated for an ideological goal (as opposed to a lone attack), and deliberately target or disregard the safety of non-combatants.
By these standards, the Sarajevo attack was terrorism only if we stretch the definition. Its purpose was to influence policy through violence, yes - Austria had been occupying Bosnia-Herzegovina against the will of most of its population for almost 40 years at that point, and had illegally annexed it in 1908. But fear didn't enter the picture. The group Princip belonged to ("Young Bosnia") wasn't firebombing schools or buses or marketplaces; they targeted the Austrian military, in the persons of its inspector-general, Archduke Franz Ferdinand, and Bosnia's military governor, Oskar Potiorek, who rode in the car with him. The civilian death - Ferdinand's wife, Countess Sophie Chotek - was entirely accidental; Princip was aiming for Potiorek, but he was a lousy shot.
Murderer he may be, but Princip is not a terrorist.
Buchanan also errs by claiming that, by provoking the war that destroyed Austria-Hungary, the assassination "succeeded beyond the wildest dreams" of its plotters. But all evidence points to this being a completely unintended consequence.
First a little historical background here. Bosnia and Herzegovina were two provinces of the Ottoman Empire (with a majority Christian population) that were placed under Austro-Hungarian occupation at the 1878 Congress of Berlin. Contrary to the provisions of that Congress and against commonly accepted law of nations at the time, Austria annexed Bosnia and Herzegovina in 1908, and administered them directly as crown lands. Obviously, this was not well received by a large Serb population, which wanted to unite with the independent kingdom of Serbia to the east.
"Young Bosnia," the organization to which Gavrilo Princip belonged, was a revolutionary society dedicated to freeing Bosnia-Herzegovina from Austrian rule and the unification of South Slavs with Serbia into a common state (following the models of Germany and Italy from the latter part of the 19th century). One of their sponsors was the "Black Hand", also known as "Union or Death," a secret society of Serbian army officers first involved in assassinating the last Obrenović king in 1903. As is obvious from their name, they also wanted the unification of South Slavs.
Now, there's a clear difference between advocating national liberation and wishing to destroy the empire that's holding one's compatriots in thralldom. The Balkans Alliance (Serbia, Montenegro, Bulgaria and Greece) that successfully defeated the Ottoman Empire in 1912 did not seek to destroy the said empire - merely to liberate the lands and peoples in the Balkans they claimed as their own. Similarly, the Black Hand or Young Bosnia - and especially the Serbian government - never thought of destroying Austria-Hungary. They were certainly interested in liberating the Serbs, Croats and Slovenes who lived under its rule. Whether the Croats and Slovenes actually wanted to be liberated is another story.
Considering that Serbia has just emerged from two years of war, it is downright foolish to assume its government was eager to fight Austria. On the other hand, elements of Austrian establishment (such Conrad von Hoetzendorf) wanted a war with Serbia rather badly, and were prepared to seize upon any pretext. They found the death of Ferdinand, who had actually kept them in check, extremely useful.
Citing Buchanan again:
"While Serbia suffered per capita losses as great as any other nation, she ended the Great War as the lead nation in a Kingdom of the South Slavs embracing Slovenes, Croats, Bosnians, Albanians, Montenegrins, Macedonians, and Hungarians. The Habsburg Empire at which Princip had struck had vanished."
Serbia lost over half of its male population to the war. One might even argue its losses per capita were greater than any other participant in the war. And while it emerged as the dominant force in the new kingdom (soon renamed Yugoslavia) after the war, that was far from a triumph. Within just a few years, Croats began to resent being removed from the Habsburg orbit. This resentment resulted in a crippling political conflict within Yugoslavia, and led to the horrific genocide perpetrated by the pro-Nazi regime of Ante Pavelić between 1941 and 1945.
Furthermore, in 1918 there was no such nation as "Bosnians," or Montenegrins, or Macedonians. People in what are today Bosnia, Montenegro and Macedonia considered themselves Serbs, Croats, Turks, even Bulgarians. It was Communist social engineering and propaganda that manufactured them into distinct "nations" - while destroying the Serbian sense of nationhood in general. I've argued elsewhere that the creation of Yugoslavia was the greatest disaster that befell the Serbs in their history, worse even than the Ottoman conquest. I shan't elaborate on that here and now, but it needs to be noted for the sake of context.
So, the event that Mr. Buchanan claims was in the same category as the 9/11 or the Mumbai attacks wasn't actually terrorism; its consequences were unintended; and it did not profit its organizers anywhere near what is commonly believed. For what it's worth, I'd appreciate historians and commentators like Buchanan not to mislabel and misinterpret it.