ALERT: Minor spoilers for the main series in this chapter. Nothing earth-shattering, but I felt it polite to mention it.
THE OPPOSING FORCES
The Turian Hierarchy
The New Territories
The military forces available to the Hierarchy greatly outmatched the entirety of the human arsenal, at least on paper. The New Territories Military Region was responsible for the defence of four garden worlds and as many as forty relay clusters, the requirements according to turian military doctrine were extensive. No less than nine fleets were stationed in the zone, of which five were directly or indirectly in Arterius' control. Turian fleets were and are smaller than human ones, built around a single dreadnought (and a single fleet carrier in the post-Contact era).
The turians could bring five dreadnoughts (two Palaven-class and three Menae-class ships), one thousand five hundred cruisers and a similar number of frigates, as well as thousands of supply and logistics vessels. Although the number of soldiers available was in the hundreds of millions, as every turian adult between sixteen and thirty-five is a soldier and everyone else is a reservist, Arterius could only call on a tiny fraction of these ships and troops without higher political authorisation. This was a significant disadvantage to any notions of simply overwhelming humanity with sheer numbers.
Two obstacles to obtaining political authorisation existed. The first was that Arterius and those generals loyal to him in his zone of responsibility had other duties to attend to. Neglecting the defence of the new garden worlds, the patrols in their clusters or the defence of the unopened relays would have seen him removed from command, aliens or no aliens. This was the reason for the dispersed efforts of the turians in the early days of the war. Instead of handling the matter personally, he told each of his direct subordinates to split off whatever forces they could and deploy them to search for the enemy. Likewise, he called in markers on Palaven, and more smaller units from a great variety of sources moved in to help.
In the end, turians from all over the Hierarchy would end up serving, on Shanxi, in space and on the many minor skirmishes on various worlds in the northwest of what is now the territory of the Systems Alliance.
The quality of these forces, despite their diverse origins, was high and almost uniform. Particularly in the planetside forces. Turian training, tactics, equipment and order of battle was standardised throughout the Hierarchy. The differences between the units that did exist were based on the personality of the commanders down through to the NCOs, and the weapons bought by the soldiers themselves. Some, like General Orinia's 43rd Marine Division, were given specialist equipment to carry out their reconnaissance and probing roles.
This had its highs and lows for the war from the turian perspective. The turians trained to fight a large scale conventional war, with more or less neat lines and a definite front to attack or defend. Theorists on Palaven had long reckoned that such a state of war could be forced on any opponent, even the asari or salarians, through use of naked military firepower. Indeed, in open ground engagements not of its choosing, humanity would find itself on the back foot.
The second reason for the lack of authorisation to simply overwhelm the Alliance defences was that any move to use more forces than those that would see action on Shanxi would draw the attention of the asari and salarians. The former in particular are now known to have very negative opinions of turian dreams of conquest, and the asari themselves ostracised figures like General Aethyta T'saza for advocating a more militaristic approach to problems like the Terminus or first contact scenarios.
Morale among the turian forces was generally low prior to the war. The turian separatist movement and the lack of action on the part of the Hierarchy to crush it had much of the younger turian population wondering what the future of their species might look like. However, once they were told they would be fighting for glory against a newly discovered species, the sense of history and duty kicked in. Most felt that they had inadequate resources for the job they were to do, which would have huge political ramifications after the war. Despite this, turians would not dishonour themselves with cowardice in combat throughout the war, and human forces often had to apply brutal means to assure victory. It was a lesson neither side would forget.
The Systems Alliance
The military forces available to humanity have been consistently underestimated in popular understandings of the war, largely because the turians possessed overwhelming superiority in numbers more broadly. However, it is false to suggest that humanity triumphed over superior numbers during the course of the conflict. Although it would have faced such numbers eventually had the asari and salarians not stepped in, the number of ships and troops that engaged were more or less even, and more crucially, humanity practised a strategy of obtaining local superiority of numbers whenever possible.
Between 2145 and 2157, human governments and then the Alliance operated under the assumption that they were very quickly going to encounter a hostile alien threat. The European Union's creation of Space Command Terra and the foundation of the Systems Alliance itself were both only possible politically and economically because of this threat. Human history is filled with instances of a technologically superior enemy invading and conquering technologically inferior cultures, starting the Neanderthals and ending with the colonialism of the 18th and 19th centuries. There was an assumption made by almost all political factions in all the major powers of Earth: any species that could reach space and use the mass effect to travel in it must be as aggressive or more so than humanity, as any species lacking this trait would have died off against competitors in its prehistory. With the singular exception of the asari, this assumption was entirely correct.
As such, Earth's nations maintained the militarism that they had found during the Cold War. Billions of humans remained under arms. Aside from colonial ventures, the entire economy of Earth was kept in preparation for total war to the largest sustainable extent. Research and development of technology with potential military applications employed five of every six scientists or high technologists between 2150 and 2157. This unprecedented phenomenon was not popular, but it was tolerated as long as it was deemed necessary. After the war, the necessity would disappear, creating discontent. It is the largest factor in why the Conservative Party of Anka Gasperi would sweep the first Alliance-wide elections in 2162.
Regardless, humanity's forces on paper exceeded those actually available to Arterius personally.
In naval strength, the Alliance outstripped the Hierarchy in the theatre of battle. The Alliance could call on six dreadnoughts of the Perseus-class and was not constrained by the need to hide their activities. Two thousand cruisers and two thousand frigates made up the backbone of the fleets, although it is important to note that Alliance cruisers were of an inferior design to their turian counterparts and the opposite was the case with frigates. These were divided into three fleets.
The First Fleet under Jon Grissom was designated for the defence of the Sol Cluster, Arcturus and other clusters with large amounts of necessary resources like eezo. The Second Fleet under Kastanie Drescher was the expeditionary force, designed to contain and retaliate against the expected alien threat. Both fleets had eight hundred cruisers. In the First Fleet, gun cruisers and carrier cruisers were equal in number. In the Second Fleet, they were weighted in a ratio of 4:3:1 for carriers, gun cruisers and planetary assault cruisers. Both fleets had three dreadnoughts each.
The Third Fleet did not have a commanding admiral, and was broken up into a hundred small exploration flotillas consisting of a pair of cruisers, a wolfpack of frigates and a number of civilian survey vessels. These were sent through relays and into the depths of each cluster in search of eezo, easily obtainable heavy metals and garden worlds. In this task, they were highly successful, leading to the second wave of human colonisation, most fatefully in the Skyllian Verge. It is one such flotilla, the 63rd Explorator, that would be present in orbit around Relay 314 when a turian patrol happened upon them.
The Alliance had one general advantage over the turians, even including the forces that Arterius was not able to bring to bear; logistics. Its supply lines were much shorter and were not crowded with the huge excess of civilian traffic seen in Citadel space. To make matters even more strange, humanity had developed better supply and troop transportation capabilities in the form of the Kodiak shuttle series and the Kowloon cargo ship series, both sporting innovations and efficiencies that made moving men and materiel from Sol to the front far more easy.
Morale in Alliance in 2157 was high, although it would suffer a great blow with the surrender of Shanxi. Only the events on that world after Williams gave the order to lay down arms would restore the fighting spirit of the species, fear being replaced by anger. The feeling that the war had finally come was almost a relief when it did, and regardless of civilian opinion, the feeling of military personnel was that this was what they had been preparing ten years for. Military psychologists have called the effect of this 'existential satisfaction' in attempting to explain the supposedly suicidal acts of defiance in the face of what appeared to be a superior enemy.
It is perhaps important to remember that neither side knew of the other's capabilities, and the war would always take a chaotic path as a result. None could predict exactly what would happen, and this coloured the political debates of both the Citadel species and of humanity. At first, Alliance forces were under-committed to the outer colonies. This was done out of a need to get a handle on the alien threat and its exact extent, a job for which committing the majority of naval and army assets was not required or desired. General Williams not possessing enough troops and ships to defend Shanxi from a relatively small turian force is one result, and it was a lesson not learned by the Alliance as late as 2170.