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If your goal really is to modernise, you might need to take on some debt to hire the expensive advisors / upgrade them to level 4 or 5 for a while. You can always pay off the debt later once you get the benefits of modernisation.
I ended up just switching out of serfdom. I don't think it's even possible to get modernization gain with serfdom.

Does switching tech group (not unit group) do anything?
 
I ended up just switching out of serfdom. I don't think it's even possible to get modernization gain with serfdom.

Does switching tech group (not unit group) do anything?
A nation's tech group determines the institution penalty it gets at the start of the game but also the military units it has available at each mil tech level. The Russian reward (mid to late game) for switching to Western is of direct benefit militarily by allowing Russian units to have the same number of pips as other western tech nations.

If you are several institutions behind, changing to western tech group may help reduce institution penalties that were driving up the costs of adoption of a new institution.
 
A nation's tech group determines the institution penalty it gets at the start of the game but also the military units it has available at each mil tech level. The Russian reward (mid to late game) for switching to Western is of direct benefit militarily by allowing Russian units to have the same number of pips as other western tech nations.

If you are several institutions behind, changing to western tech group may help reduce institution penalties that were driving up the costs of adoption of a new institution.
I'm talking about that Russian mission, but it doesn't change unit type.
 
I'm talking about that Russian mission, but it doesn't change unit type.
Completing the mission Westernize the Military triggers the event which changes the unit type.

Changing the tech group does not have much of an impact. You get neighbor discounts for tech for all nations in your tech group even if they are not neighbors. And the discovery of provinces spreads to you a certain number of years after it was discovered by somebody in your tech group(not sure if it is 50 years or 100).
 
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I have 1500+ hours in eu4 and I still don't understand personal unions.
Currently I'm trying to do "The Burgundian Conquest" achievement. It requires having France and Austria as subjects. I decided to eventually annex France, and to try to PU Austria. The dynasty barely spreads, though.
As far as I'm aware, there is random chance that dynasty spreads through royal marriages, but it seems unreliable because base heir chance is pretty high. There is also "request heir" option that I use whenever there is a n opportunity; but it requires 90 favors with target country, which means having an alliance, and then AI likes to disinherit or to assign heirs as generals. And even after the dynasty spreads, you have to break the alliance and wait 5 years, during which their successions stops being disputed. There is technically a possibility of forming PU peacefully, but outside of scripted events I haven's seen it once. Overall, it seems to RING-dependent and slow. Is there anything else I am missing?
The save:
 

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to try to PU Austria. The dynasty barely spreads, though.
PUing Austria without a mission tree CB is especially difficult, because they are likely to return to the Habsburg dynasty with the event The Habsburg Dynasty. It is probably easier if you let the Habsburg dynasty spread to your country by letting your ruler die without an heir while they are the most eligible country to spread their dynasty(you can avoid getting PUed by them by either having a junior partner yourself or by being at war during the phases in which a PU occurs).

For more details I suggest checking out various PU guides or the following infographic https://drive.google.com/file/d/10jiz4vSY0UFGVVaMi2nmqXjs9wL1wRQN/view
 
PUing Austria without a mission tree CB is especially difficult, because they are likely to return to the Habsburg dynasty with the event The Habsburg Dynasty. It is probably easier if you let the Habsburg dynasty spread to your country by letting your ruler die without an heir while they are the most eligible country to spread their dynasty(you can avoid getting PUed by them by either having a junior partner yourself or by being at war during the phases in which a PU occurs).

For more details I suggest checking out various PU guides or the following infographic https://drive.google.com/file/d/10jiz4vSY0UFGVVaMi2nmqXjs9wL1wRQN/view
That explains how they kicked out two of my heirs. Anyway, I did establish the PU.

Screenshot from 2025-10-20 00-26-38.png

Oh wow, that phase counter is absolutely awful.
 
just upgraded laptop, better bigger screen - but in-game text too small;
how do i adjust it
thanks
There is a GUI scale option in the video settings. But it results don't look very good. If you have a resolution of at least 1440p, you can try the mod Proper 2K UI Enhanced. If it is just the text, you can try some font mods which replace the default font with one which is easier to read. Or you can play on a lower resolution or check if your GPU has an option to scale the game