Studies in the "Foreign expertise" tab in the Academy are now divided into two stages.

The first stage unlocks once the Academy has been upgraded to level 31 and contains three categories: Attacking, Defending, and Castles I.
 

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The second stage of Studies appears in the same tab at Academy level 36 and contains six new categories: Offense, Defense, Health, Castles II, Towns, and Tier VIII Warriors.
 

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The mechanics for increasing the cost of Studies apply to both the first and second stages. This means that, initially, the cost in all categories starts at the first level, but once you have conducted a Study in one category, the cost for all remaining categories increases to the second level.

For example, if you conduct a Study in the Towns category, then the cost of Studies in the Offense, Defense, Health, Castles II, and Tier VIII Warriors categories will increase. 

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When you conduct a Study in the next category, the cost of the remaining categories also increases. Let's say that, after Towns, you conduct a Study in the Castles II category. Then the cost of the Offense, Defense, Health, and Tier VIII Warriors categories will increase to level three.

Conducting a Study in yet another category will increase the cost for the remaining categories to level four, etc. Consider your development strategy carefully and choose Studies that you need to prioritize beforehand.

It's important to note that the cost increases for categories of the first and second stages are not related at all. Thus, conducting Studies from the first stage doesn't increase the cost of Studies from the second stage.

Imperial Fury

Imperial Fury is a Study in the Towns category from the second stage of the "Foreign expertise" tab. It gives a substantial bonus to the offense of your troops when attacking Towns but prevents you from using Inaccessibility for a while.

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With every level of the Imperial Fury Study, both the bonus to the offense of your troops and the time during which you cannot use Inaccessibility increase.

After you've conducted the Study, you cannot prevent its bonus from activating!
 

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All Studies in the "Foreign expertise" tab can be conducted in exchange for either Trophies of Arms or Gold. When using the former, the upgrade process will take some time, while the latter will allow the Study to be conducted instantly.