I once heard from a teacher that one of the main reasons that explorers from Portugal and Spain sailed out into the Atlantic or around Africa to find a passage to India was because the spice trade had been effectively cut off from Western Europe by the Ottomans after they took Constantinople in 1453. Is this actually true? Did the Ottomans impose any extra tariffs or try to limit the flow of goods west? Was this a major factor that encouraged seafaring expeditions, or were other factors more important?
Thanks!
Common claim, but the truth was more complicated.
Most of the European trading houses were already doing business with the Ottomans before the fall of Constantinople, as the Ottomans controlled most of the ports elsewhere in Asia Minor along the Aegean, and were also making a hefty profit off of facilitating the trade This is one of the things about the "the Ottomans cut off the supply" argument that's non-sensical -- part of the reason they wanted to dominate was to control the trade and make money off of the taxes that they collected from it. Providing safe routes for traders coming in from the east was hugely important to them -- you can still see the caravanserais (inns) along the old trade routes throughout modern Turkey that the Ottoman state built to keep traders and their goods safe.
The issue is that the Ottomans were trading with Venice and Genoa (at times one, at times the other, at times both), and between them they had a monopoly that guaranteed that the Ottomans and their European trading partners could essentially charge whatever they wanted because there was a willing market in the rest of Europe. The fact that the Ottomans had European trading partners tends to get dropped from the story because it complicates things.
So, first Portugal and then Spain, which developed strong navies in the Western Mediterranean in the late 1400s, decided to try going around Africa to reach India on their own--not, as the story often goes, to try to restart the trade or free it up--but to try to cut the Ottoman/Genoese/Venetian trading block off and get a piece of the pie for themselves.
And, yes, this was one of the issues that motivated the Spanish (er, Leonese and Castillan-- it wasn't quite Spain yet) crown to finance Columbus's expedition -- the fall of Granada in January 1492 meant that the state was no longer paying for a never-ending war and could take a gamble on this crazy guy who thought Asia could be reached by sailing westward. In fact, Columbus specifically had orders to report back on potential trading partners who might be recruited for a war against the Ottomans that would be waged from both east and west -- of course, he found no such thing, but that was originally part of his mandate.
Check out Giancarlo Casale's The Ottoman Age of Exploration for more of this -- it's quite an interesting story.
In addition to the answer you've already got, u/terminus-trantor has also covered this topic before in the following threads::
They've also covered it over on r/badhistory: