These diplomatic talks occurred in the wake of the Krogan Rebellions, as a response to the destruction of the conflict and an attempt to distance the Council from the brutal krogan warfare.
The Conventions regulate the use of Weapons of Mass Destruction. A WMD causes environmental alteration to a world. A bomb that produces a large crater is not considered a WMD; a bomb that causes a "nuclear winter" is.
Use of WMD is forbidden on "garden" worlds like Earth, with ecospheres that can readily support a population. If a habitable world is destroyed, it will not be replaced for millions of years. The Conventions do not forbid the use of WMD on hostile worlds or in sealed space-station environments. Many militaries continue to develop and maintain stockpiles.
The Conventions graded Weapons of Mass Destruction into tiers of concern. Tier I is the greatest threat to galactic peace.
TIER I: Large kinetic impacters, such as asteroid drops or de-orbited space stations. Effectively free and available in any system (in the form of debris left over from planetary accretion), kinetic impacters are the weapons of choice for terrorists and "third galaxy" nations.
TIER II: Uncontrolled self-replicating weapons, such as nanotechnology, viral or bacteriological organisms, "Von Neumann devices", and destructive computer viruses. These weapons can lie dormant for millennia, waiting for a careless visitor to carry them on to another world.
TIER III: Large energy-burst weapons such as nuclear or antimatter warheads.
TIER IV: Alien species deliberately introduced to crowd out native forms necessary for the health of an ecosystem. Ecological tampering can take years to bear fruit, making it difficult to prove.