Modern space combat is a ponderous affair, not only is the chance of a round striking an enemy ship rather slim, going on improbable at extreme ranges, a hit from a mass accelerator is not guaranteed to destroy a ship. This is due to kinetic barriers being able to absorb large amounts of kinetic energy. While a single shot from a similarly sized vessel will drain the majority of a kinetic barrier's capacitors, or simply damage the emitters from the stress, those can be recharged or repaired rather quickly, leading to the barrier commonly being at full strength when another shot manages to hit.
Solutions have been tried for millenia, with expendable munitions being at the forefront of attempts. While munitions were in use, with nukes, conventional missiles, and expendable lasers (both nuclear based and not) being the most common, they never proved powerful enough to challenge the supremacy of the mass accelerator, being relegated to secondary weapons used when the range closed or in unique circumstances.
This was changed by the invention of the disruptor by humanity, a simple but game changing discovery that almost turned space combat on its head. A disruptor is simply a small eezo core with a large capacitor holding vast amounts of energy. When a disruptor warhead reaches a ship's kinetic barriers, the eezo core within it detonates, having been overloaded beyond what the eezo can take. The explosion itself does not do much damage, but the highly excited eezo reacts with the mass effect field produced by the kinetic barrier emitters, and stresses the emitters, causing disproportionate damage to them and, with enough strikes, overloading them.
There are of course problems, in order for the disruption effect to take place, the eezo from the warhead needs to, for lack of a better word, "resonate" with the mass effect field formed by the emitters, leading to the eezo needing to be negatively charged, which increases the mass of the warhead and its delivery mechanism (usually a missile or torpedo, though some tests of using mass accelerators have been done), while lowering the velocity. The long time it takes to overcharge an eezo core means that the munition is affected by the change in velocity and mass while still closing with the target, making the munition much more susceptible to interception. This is counteracted by the relative simplicity of the disruptor, and the relatively low amount of total disruption needed for most ships, allowing for them to be made very small, in large numbers, while retaining their effectiveness. The problem of needing to reach the target was mitigated by the invention of the Javelin Disruptor Torpedo System, which launches disruptor torpedoes in pairs that can resonate on their own, simply letting the emitter be caught in the crossfire. This system allows for warheads to detonate even several kilometers away from a ship, and still damage its barriers, increasing the rate of disruptor torpedoes damaging a target greatly, while also allowing Fighters to launch torpedoes further away while retaining effectiveness, lowering Fighter losses due to point defenses considerably.
The disruptor is a good weapon for stripping the shields of targets, and is not too bad at striking unshielded targets. The disruptor gave a powerful edge to Fighters and other small warships against the Cruisers and Dreadnoughts that have dominated combat for millenia, changing the dynamics of space combat. Fighters were not the only craft helped by the disruptor, Frigates gained a new prominence as the disruptor both gave the small warships a new weapons against larger craft (allowing them to truly damage such vessels instead of simply swooping down on those which lost their barriers like carrion birds, though less effective than Fighters), while also creating a new threat for them to defend fleets against (while Frigates are not that effective alone against a Fighter swarm, a sphere of them provides a decent amount of point defenses for the cost, while also being able to fire those defenses long than larger vessels because of their better heat management). The introduction of the disruptor saw an increase in the prevalence of Frigates alongside the Fighter.
Since the introduction of the disruptor, point defenses and Fighter compliments have increased on newer designs, with many older designs being retrofitted to allow them more protection from the newly empowered small craft. Of course, this only started after first contact, as no one in Citadel space knew of the newly born threat until they learned of humanity.