Because the Empire of Valencia is the strongest amongst both factions, though not combined, is placed at the head. They also have the strongest say on coordinating military action on land.
The Kingdom of Trinidad has a lot of power at its disposal ever since it formed, putting the southern powers at a disadvantage when colonies began emerging. In order to have a better fighting chance of not being overshadowed, the Triumvirate Alliance came to be. The agreement is that all three core powers are to unite in their efforts and push things in their favor.
Benefits of Specializations
Each member of the Triumvirate has their own specialization. This is to compensate for the lack of resources that allow them to diversify their strategies. Compared to their mortal enemy, the Kingdom of Trinidad, it's far from a standardized and uniform mess. Of course, the allies do have uniform standards but this specialization keeps them less predictable.
The Valencian Backbone
Valencia is the powerhouse of the Triumvirate. Their production and land doctrines are superior to their allies. Sharing this information helps keep their efforts sustained and disciplined but it's not as useful if they intend on specializing.
The Madrian Explorers[ p]Madrians are bold and curious. That is why they expertise in taking on the seas. Their navy and map-making keep the Triumvirate updated on their plans and operations.
The Venezian Arcanists
The mysterious Venezians are great at subversion and the arcane. Their knowledge may not be as vibrant as Vrexen's but it does offer a different perspective. As such, they utilize magic in their subversive efforts. They also have soldiers who utilize their arcane arts in battle, allowing for unpredictable strikes on the enemy.
Trade & Transport
Privileges of Membership
Each member of the Triumvirate has free reign to simply walk through each other's borders as if it were one country. This allows trade within to flourish without the hindrance of bureaucracy.
Trade is also emphasized to stay within the alliance. Trading with non-members is acceptable but they will not be exempted from the taxes that are imposed as a standard. The idea is to help encourage cooperation with each ally.
The Society of Negotiations in the Orian, or SNO for short, is the official trading company of the alliance.