At this point imperium seems to function largely off the number of technologies you have researched. Taking settlements, tributary states, and resettling razed sites effect Imperium at a much slower rate by comparison.

Acquiring a settlement through ownership or tributary state will increase your imperium by a sliver of the imperium bar. It is almost imperceptible.

Researching a technology seems to have 10 times the effect as settlement acquisition, you will certainly notice a change in the imperium bar. Since technology times and turn times get longer as the game rolls on, the technology effect slows down when compared to early game. Tech still effects imperium by the same increment, it just ticks by much slower.

I am unsure at this point if maxing tech will max your imperium or if acquiring settlements is necessary to achieve this. If anyone knows pls share, thanks.

I can only speculate that CA chose to have Imperium increase based on tech for the migratory factions, and of course, the Huns who can never settle. In Rome 2 Imperium was exclusively driven by the number of settlements you held, an obvious problem for the antagonist and namesake of the game, Attila and his Huns.

Imperium effects the number of armies, fleets, agents, and governors you can have. Governors are likely the most important facet of Imperium in regards to your faction.

Imperium can effect the loyalty of your characters (generals, statesmen, etc). Unfortunately I failed to verify if this was related to a trait, and what trait. I just had the guy killed and moved on, oops.

Imperium will have a very heavy effect of diplomacy. Leaders of rival factions can view you in drastically different ways based off their personal traits, visible in the diplomacy window. There are four important distinctions in traits.

• Hates Rival Empires: This guy will have -75 on his view of you denoted as "Great Power" in the list.
  
• Indifferent to Rival Empires: For this guy "Great Power" will likely be a single digit.
  
• Admires Strong Empirs: This guy will have +30 "Great Power"
  
• No Distinction: if a leader has no reference to an empire he will have -30 "Great Power".

These numbers are based off imperium 3.

• The base modifier is your imperium level x -10. So at imperium 3 you will have -30 great power base, at imperium 4 you will have -40 base.
  
• Hates takes your base and multiplies it by 2.5. So imperium 4 base modifier -40 x 2.5 = -100.
  
• Indifferent takes your base and multiplies it by 0.25. Imperium 4 base modifier -40 x .25 = -10
  
• Admires takes your base and multiplies it by -0.75. Imperium 4 base modifier -40 x -.75 = 30

There is a strange wild card where "Hates" will have -80 instead of -100 at imperium 4. I cannot figure it out for the life of me. I looked at traits, treaties, wars, etc, i see no correlations. Also I'll be the first to admit I'm terrible at math, so if I wrote something wrong I'm depending on one of you math nerds to let me know, thanks =)

• Raising Imperium can have a very negative effect on diplomacy if the rival faction leader has the trait "Hates Rival Empires" with the subtext that he hates any faction who's impearialsm threatens his expansion. You can deal with this guy by using an agent to assassinate him or simply find and kill him on the battlefield. Both are a gamble as his heir could have the same trait, and going to war to kill a general in counter productive in the short term.
  
  
• Another option is to not do research, somewhat freezing your imperium at a desired level while you build a strong enough base from which to expand. The fact that the Minor Victory lists 10 techs researched as a condition insinuates this as 20 techs by 425 AD is easy to achieve.
  
  
• Lastly blanket research is nice for the tier bonus, but it will ramp your Imperium up very fast. It maybe wiser to go into longer research paths to get the most out of your Imperium (such as going for Manoral Lands to help with food issues and unlock Viking Raiders for the military when playing as a viking forefather.).

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