The old formula used by many imperialists, especially the British Empire, is to carve up states that pursue independent policies with the hope of replacing the weakened governments of these new states with lackeys who will better serve the imperialists. This has been a plan for Iraq (which was partially implemented with a semi-independent Kurdish province) and now Syria for quite some time.
As many geopolitical observers like Pepe Escobar have pointed out, another major reason to divide up Syria was their government's refusal to go along with the Qatar's proposed pipeline that would transport gas from their fields to Europe. Escobar wrote in 2015 referring to the war in Syria:
Kissinger then claimed that the current Syria was conceived as a more or less artificial national unity consisting of different tribes and ethnic groups.
This same theory was also presented by the Israeli Oded Yinon plan which is an article published in February 1982 in the Hebrew journal Kivunim ("Directions") entitled A Strategy for Israel in the 1980s. This plan is an early example of characterizing political projects in the Middle East in terms of a logic of sectarian divisions and the dissolution of all the existing Arab states.
Hence, supporting the partitioning of Syria began with the US and Israel’s full support of the so- called “Rojava Project”.
Well the Empire builders would not permit this to happen because the Syrian government's plan would benefit their arch-enemy Iran. Then China's government came up with other plans. As an article sourced from Washington's Blog explained explained about the competing interests:
Damascus, instead, chose in 2010 to privilege a competing project, the $10 billion Iran-Iraq-Syria, also know as «Islamic pipeline». The deal was formally announced in July 2011, when the Syrian tragedy was already in motion. In 2012, a Memorandum of Understanding (MoU) was signed with Iran.
Indeed, the “Great Game” being played right now by the world powers largely boils down to the United States and Russia fighting for control over Eurasian oil and gas resources:
Russia and the USA have been in a state of competition in this region, ever since the former Soviet Union split up, and Russia is adamant on keeping the Americans out of its Central Asian backyard. Russia aims to increase European gas dominance on its resources whereas the US wants the European Union (EU) to diversify its energy supply, primarily away from Russian dominance. There are already around three major Russian pipelines that are supplying energy to Europe and Russia has planned two new pipelines.The rising power China is also getting into this Great Game:
The third “big player” in this New Great Game is China, soon to be the world’s biggest energy consumer, which is already importing gas from Turkmenistan via Kazakhstan and Uzbekistan to its Xinjiang province — known as the Central Asia-China Pipeline — which may tilt the balance towards Asia. Pepe Escobar calls it the opening of the 21st century Silk Road in 2009 when this pipeline became operational. China’s need for energy is projected to increase by 150 per cent which explains why it has signed probably the largest number of deals not just with the Central Asian republics but also with the heavily sanctioned Iran and even Afghanistan. China has planned around five west-east gas pipelines, within China, of which one is operational (domestically from Xinjiang to Shanghai) and others are under construction and will be connected to Central Asian gas reserves.