Adding Spain and Brazil destabilizes Washington treaty arithmetic

Could a stronger Spain or Brazil have joined the Washington Naval Treaty, and would France and Italy accept equal tonnage for them?

They could plausibly gain seats, especially a six-battleship Spain, but not simple equality with France and Italy; the treaty would need an expanded tier system that compensates France and reshapes every major power's allowance.

Spain is the more plausible additional treaty power if it completes three larger dreadnoughts alongside the Espana class and accelerates its cruiser program, giving it roughly six capital ships and a credible industrial base. Brazil could qualify through its existing dreadnoughts and a stronger cruiser force, though it would be less likely to build to its full allowance. The central obstacle is France: granting Spain a substantial Mediterranean tonnage complicates an already difficult parity with Italy and could trap the French fleet between two treaty-limited neighbors. One possible system gives Britain and the United States twenty capital ships, Japan fourteen, France and Italy about eight each, and Spain and Brazil perhaps four modern 35,000-ton equivalents. Those higher ceilings would permit new British, American, Japanese, French, and Italian construction, possibly encouraging faster battleship designs. Ordering five ships instead of two could also make a reduction in individual armor more acceptable because more hulls would share the fleet's duties. Every added navy alters the security calculations and construction choices of all the others, so treaty ratios cannot be treated as abstract rankings.