Given the task definition and input, reply with output. This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

The economic structure of the Empire was defined by its geopolitical structure. The Ottoman Empire stood between the West and the East, thus blocking the land route eastward and forcing Spanish and Portuguese navigators to set sail in search of a new route to the Orient. The Empire controlled the spice route that Marco Polo once used. When Vasco da Gama bypassed Ottoman controlled routes and established direct trade links with India in 1498, and Christopher Columbus first journeyed to the Bahamas in 1492, the Ottoman Empire was at its zenith.
What serviced as the foundation for the structure of the economy of the Ottoman empire?