The Baghdad Railway
Since the Baghdad Railway was a very important German project for the connection of Germany with the Persian Gulf (see red line on the following map) I must say a few words about it.
Note! Even thought the Baghdad Railway would follow the route of what today is Germany-Czech Rep-Austria-Hungary-Serbia-Bulgaria-Turkey-Syria-Iraq, and would pass from Baghdad and Basra, my red lines on the maps are rough and not exact lines.
For some people the Baghdad Railway was the real cause of the First World War, since it is this very railway that would connect Germany to the Persian Gulf, also bringing Germany close to India. I think it seems more appropriate to consider Germany"s wish to expand to the Persian Gulf as the cause of the war, than to consider the Baghdad Railway as the cause of the war.
What was important was the decision of the Germans to expand to the Persian Gulf, not the actual way they would do so. Whether this connection would be achieved by the Baghdad Railway or some other means, it seems to be of secondary importance. However nobody can deny that the Baghdad Railway was very important, and therefore I will provide some Wikipedia sources to demonstrate that this is so.
You can read at the following Wikipedia link that the construction of the Baghdad Railway started in 1903 and was completed in 1940, and its aim was to connect the German Empire to the Persian Gulf, because the Germans wanted to acquire control of a port in the Persian Gulf. Please note that the project started in 1903, and the English and the French closed their differences with the Entente Cordiale in 1904, and the English and the Russians closed their differences in 1907.
https://en.wikipedia.org/wiki/Baghdad_Railway
At the end of the 3rd paragraph of the following Wikipedia link, you can read that the Germans had managed to obtain ownership of some oil fields in Iraq, and with a railway to Basra they could obtain oil supplies while avoiding the sea lanes and the Suez Canal, where the British Navy was dominant. At the same time, they could use the Persian Gulf to export their products to Asian countries.
Therefore this railway would have two roles. The first one would be to supply the German industry and the German army with oil, and the second to transport the German products to the Persian Gulf, and from the Persian Gulf to export them to the Asian countries, India included.
https://en.wikipedia.org/wiki/Baghdad_Railway
More specifically, according to Wikipedia:
“The Germans gained access to and ownership of oil fields in Iraq, and with a line to the port of
Basra would have gained better access to the eastern parts of the German colonial empire, by avoiding the Suez Canal”.
In the beginning of the 4th paragraph of the following link, you can read that the Baghdad Railway had become a source of tension in the years before WW1.
“The railway became a source of international disputes during the years immediately preceding World
https://en.wikipedia.org/wiki/Baghdad_Railway
In the first paragraph of the following Wikipedia link, in section "Overview", you can read that the Baghdad Railway would offer the German Empire safe access to oil by avoiding the British Navy.
https://en.wikipedia.org/wiki/Baghdad_Railway#Overview
At the second paragraph of the same Wikipedia link, you can read that the Baghdad Railway was also a threat to Russia, since it would offer the German Empire access to the Caucasus Mountain. Caucasus is located next to the oil rich Caspian Sea region, which was controlled by the Russians.
https://en.wikipedia.org/wiki/Baghdad_Railway#Overview
Moreover in the beginning of the 4th paragraph of the following Wikipedia link, it is mentioned that as early as 1871, geologists had already discovered rich and high quality oil fields in the area of Mesopotamia (Iraq), which was at the time part of the Ottoman Empire.
https://en.wikipedia.org/wiki/Baghdad_Railway#Overview
At the paragraph before the last one in the following Wikipedia link, you can read that as early as 1903 there was unrest in France, England and Russia for the beginning of the Baghdad Railway.
http://en.wikipedia.org/wiki/Baghdad_Railway#The_Baghdad_Concession
In the first line of section "After the War" of the following Wikipedia link, you can read that after the end of WW1, with the Treaty of Versailles, Germany was stripped from the ownership of the Baghdad Railway (Deutsche Bank was a larger investor in this project).
http://en.wikipedia.org/wiki/Baghdad_Railway#After_the_war
In the last line of the 3rd paragraph of the following Wikipedia link, you can read that there were negotiations between the English and the Germans before WW1 regarding the Baghdad Railway, and the Germans had agreed to allow some Englishmen in the board of directors, in order to ensure that the railway would not rich the Persian Gulf.
This is actually the reason that some people believe that this railway was not the cause of WW1, since the Germans and the English had an agreement about it. However I do not think that a paper agreement would make the English and the Russians feel very secure.
https://en.wikipedia.org/wiki/Causes_of_World_War_I#International_relations
And like if all these disputes for the Iraqi and the Baku oil were not enough, in 1908 oil was discovered in Iran too, as you can read in the following Wikipedia link, further increasing the geopolitical importance of the region.
https://en.wikipedia.org/wiki/Anglo-Persian_Oil_Company
If you wonder why Saudi Arabia, which is the king of oil, is not mentioned at all in my essay, it is because the first important oil field of Saudi Arabia was discovered in 1938. As you can see on the following map, at the beginning of WW1 the interior of the Arabian Peninsula (Saudi Arabia) was not controlled by any great power since oil had not been discovered yet. The Ottomans and the English were only controlling its outer parts which were important for controlling the sea lanes.
As you can read in section "Before the discovery of oil" of the following Wikipedia link, the consensus at the beginning of the 20th Century (1900), was that there was not oil in the Arabian Peninsula.
https://en.wikipedia.org/wiki/History_of_the_oil_industry_in_Saudi_Arabia
As you can read in section "Discovery of Oil" of the following Wikipedia link, oil was finally discovered in Saudi Arabia in 1938.
https://en.wikipedia.org/wiki/History_of_the_oil_industry_in_Saudi_Arabia