To be a great global empire requires that there be meaningful alliances with allied or like-minded countries, or else it will eventually fall apart, because without those alliances, there are just too many areas that are exposed for other non-aligned nations to exploit to their own advantage and thus nibble away at that empire, all leading to the decline and probable ultimate destruction of the same.
History tells us that great empires cannot last unless they form alliances either on friendly terms with other countries or have those nations that have been conquered be amenable to working within the structure of that empire for the betterment of all parties. Indeed, in a world this large and with competing interests, it is thus imperative to have solid alliances based upon the fact that in numbers and strategic planning that those that are aligned are going to be in a better place then if they were separate or structured in a way that the weaker party was forever in the subservient role, as compared to having their fair say, which plays not only better with such an alliance, but benefits their own people, as well.
Additionally, no nation and no person of merit, appreciates being lorded over, because not only does this build resentment but it belittles the other, and makes the other to consider alternatives and options that might be better than the way that things are, which signifies that an empire needs not so much to have a puppet government in its hands, but rather requires that each party sees and feels the clear benefit of aligning with one another, or else it will come apart, sooner or later.
Indeed, we shouldn’t expect that aligned nations that find an empire to be overbearing and a burden upon them will decide to give their best effort in defense of that alliance if they rightly believe that they aren’t getting the consideration and respect that they deserve, because for an empire to be strong and vibrant, this necessitates a true buy-in from other nations, which means that they must have a seat at the table, rather than being reduced to an irrelevancy or compelled to be obedient, which creates not only resentment but the seeds of an alignment that will sever itself from that empire, eventually.
So too, it has to be acknowledged that other countries typically have control or access to vital resources that are beneficial to having that strong alliance, for without such, other non-aligned nations are surely going to look for vulnerabilities within any empire, and through those vulnerabilities be able to place themselves in a position in which they can weaken that empire, because when necessary vital resources are lacking, empires begin to frail at the edges.
Those who desire to be an empire need to comprehend that might only takes an empire so far, because when there are few true allies, or those that are allied are consistently pushed about and disrespected, then it makes that empire be structured in a way and manner that it will not exist in perpetuity because it has not won over those that it needs to win over, but merely has papered over the faults that will eventually serve to erode its power and influence, over time.