Farixen Naval Treaty of 1182
Overview
The lack of restrictions allowed the Krogan Imperial war machine to grow unchecked in the decades leading up to the Krogan Rebellions, until Krogan naval power reached a point where it rivaled both the asari and salarian navies combined.
Following the end of the Rebellions the Farixen Naval Treaty of 1182 was written up in 788 CE. The purpose of the treaty was to prevent a second Krogan Rebellion by enacting limitations on warship construction and ensuring that no race would be legally allowed to possess the naval power necessary to wage war against the Citadel and/or overthrow the Citadel Council.
The treaty dictates limitations on Dreadnought construction and provides clear classifications for ship types.
Though, initially signed by only a handful of races, signing the treaty has become a requirement for any race wishing to open an embassy on the Citadel and have a voice in galactic politics.
Dreadnoughts
As defined by the treaty, "A dreadnought is a capital ship with a spinal mounted main gun and a hull length in excess of 800 meters."
The restrictions of the treaty of Farixen prevent Dreadnought construction from exceeding a hull length of 1 kilometer. The combined firepower of a Dreadnought's secondary guns can not exceed 2.2x the power of their main gun.
Due to their emens firepower of a dreadnought, a ratio is fixed between the Citadel races to limit the number of dreadnoughts any race is allowed to construct in proportion to the Council races. The ratio of turian, to Council to associate member is 5:3:1. For every 5 dreadnoughts the turians are allowed to build, the asari and salarians have 3 and all other races that recognize Citadel authority have one.
When humanity signed the treaty in 2157, they already had three dreadnoughts that they had built prior to their introduction to galactic society. These Dreadnoughts possessed two spinal mounted main guns that ran 90% of their 888 meter hull Length. This was technically a violation of the treaty. However, the Citadel let it slid due to how underguned the ships were when it came to secondary weapons. Even if the second main gun were considered part of the secondary armament, it still doesn't come close to the 2.2 rule stated in the treaty.
Humanity's second class of Kilimanjaro-class dreadnoughts commissioned a few years later would remove the second main gun, but push the upper limits of the other restrictions the treaty. Coming in with a hull length just four meters short of the maximum length, allowing it to carry the longest main gun of any other Citadel ship and a combined secondary armament 2.13x the power of the main gun, it was the second largest Citadel ship and the third most powerful.
The Systems Alliance would quickly max out the number of dreadnoughts they were allowed to build by building three Kilimanjaro-classes in addition to the three Everest-classes they had, with a fourth Kilimanjaro-class under construction. The idea was to then retire the Everest-class and replace them with newer ships. This changed in 2183, when humanity joined the Citadel Council and were now allowed to build up to 22 dreadnoughts and 23 later after the turians expanded their fleet. This led to a massive boost in dreadnought construction to catch up. With three new Kilimanjaro-class dreadnoughts being completed in as many years.
The 2160s also saw the baterians, who were no longer restricted by the treaty of Farixen, construct their first dreadnoughts in over a century in response to growing hostilities between the Human Systems Alliance and Baterian Hegemony. They HSN Glory of Kar'shan and HSN Hegemony's might were the pride of the Hegemony Superior Navy. However, with the Baterian Hegemony lacking the funds to field a proper dreadnought force, the Kar'shan-class dreadnought was built on the cheap. In addition to a myriad of operational issues, they were also dreadnoughts in name only and nothing else. Though they had hulls that were 804 meters long and a spinal mounted gun, they were poorly armoured and had firepower comparable to a heavy cruiser (when the guns are all operational) Alliance Intelligence also suggests that the coils of a Kar'shan-class dreadnought's guns had a tendency to melt due to faulty heat management, with almost half the armament prone to failure during combat.
The geth also don't adhere to the treaty and in addition to having dreadnoughts above the legal limit, they are also believed to have as many dreadnoughts as the turians.
In 2183, the turians had 37 dreadnoughts and made up the bulk of the Citadel peacekeeping force, the asari had 21 and the salarians had 16. Humanity had 6 with their seventh and last dreadnought under construction. The baterians also had 2.
by 2186, the turians had two more dreadnoughts, the asari lost one and humanity had built three more with upto a dozen more planned. The turians had also built a dreadnought to be sold to the volus.
The quarians had armed all their ships, including their 3 km liveships, which were now dreadnoughts (at least from a firepower standpoint). A decision that drew a ire from other races due to it's violation of the treaty of Farixen. But no legal action could be pursued due to the fact that the quarians were no longer restricted by the treaty.
Cruisers
As defined by the treaty, "A Cruiser is a warship with a spinal mounted main gun and a length between 300 meters and 800 meters."
Like dreadnoughts, cruisers were restricted to a combined secondary armament no more powerful that 2.2x that of the main gun.
Cruisers didn't have a limitation on numbers and were typically the largest ship present in most navies.
Like their dreadnoughts, early Alliance cruisers had two main guns. Though a violation of the treaty, this, they also let slide, due to the limited power of their secondary guns. Later Alliance Cruisers would remove the second main gun in favor of having as many secondary guns as the treaty allowed.
Frigates
As defined by the treaty, "A Frigate is a warship with a spinal mounted main gun and a length between 100 and 300 meters."
Restrictions prevented Frigates from having secondary weapons entirely, but this only applied to fixed weapons, not turrets, missiles or torpedos.
Frigates were the most numerous ships used by any species.
Corvettes
As defined by the treaty, "A Corvette is a heavily armed warship measuring between 50 and 100 meters in length."
Corvettes are the largest military vessel to be classified as a warship. Anything smaller is classified as a Combat Support Craft or Fast Attack Craft.
Miscellaneous
Species under the restrictions of the Treaty of Farixen are not allowed to construct civilian ships equiped with or with the capacity to equip spinal mounted weaponry that could give it the capabilities of a dreadnought.
Fighter carriers are exempt from the restrictions of the Treaty of Farixen as they did not exist as a concept when the treaty was written. As long as they don't have any spinal mounted weapons, a carrier can be just as large, if not larger, than a dreadnought.