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How to Make a Country
This guide will direct you through the process of creating a new country whose given culture already exists. The guide contains information for both countries that will be on the map upon starting a new game and countries who can be released by their current owner or formed through another country waging war on the owner with the wargoal "Free ____ in ____" This guide will make Byelorus a playable nation as an example.
Finding the Files
The first step is to find the files you will be editing. Go to My Computer and access your C: Drive. Open up program files (or program files x86) It may be under Steam --> Common --> Victoria 2 if you downloaded the game off of Steam, but if not it will be under the Paradox Interactive folder. It is strongly recommended that you make a back-up. Simply hold ctrl and drag a copy to your desktop. Let's choose to edit the files in the Victoria 2 folder in program files. Rename the one on your desktop something that will let you know it is a backup. Open up the folder in the Paradox Interactive/Steamapps folder and begin.
Creating the Country
In the Victoria 2 folder, find the folder named "common" and open it. First open the .txt file (NOT THE FOLDER) named "countries". Find the category that the country you are trying to make best fits into. For Byelorus, let's go with # Eastern Europe. Create a new line somewhere in the block and type a three letter tag. The tag must be three upper case letters. It cannot be taken by another country (Prime grounds for not naming the country "Belarus" and entering a name conflict with "Belgium"). Ctrl-F and type in the tag you chose to verify that your tag is not already taken. The tag "BYE" is not. So in a new line under CZH we will type BYE. Then hit the tab key twice and type following the format of the lines above: = "countries/Byelorus.txt" Save and close this document.
Now go back and find the folder named countries. Inside will be .txt files of every playable country in the game. To make a .txt for the new country, pick the country most similar to the one you aim to make. For Byelorus - let's go with Russia. Hold ctrl and drag Russia to make a copy of it. Rename the "Russia - copy" file to "Byelorus" and then click on it.
The first line is the country's color - what shows up on the political map. It's in RGB format, if you are familiar with it. If not, the first number is red, the second green, and the third blue. The numbers are a scale of 0 to 255 0 being devoid of that color, 255 being the highest amount. Play around until you find what you want, or copy the numbers from a "custom color selection" in MS Paint. The second line is the Graphic culture. Keep it what it is for Byelorus. Despite any desire to go in depth with developing your country, leave the RUS tag on the party names. If you change it to BYE you will have to make changes later. Besides, Byelorussian political parties can't be too different from Russian political parties, can they? Save and close this document.
Now go into the "history" folder and find the file named RUS - Russia. Make a copy of it and rename it it to BYE - Byelorus. First thing's first, the capital can't be Moscow. Look up the province number for the capital of Byelorus - Minsk, which is 718. Next, change the primary and secondary cultures. The words are always lowercase. If you want less accepted cultures, simply delete the line. Let's go with byelorussian as primary and russian as secondary. If you really want you can make polish or ukrainian accepted cultures, too. Let's keep religion and government type the same. Under that block of text will be something with the phrase Great Power. Delete that line. In the next line, set the prestige for Byelorus. Russia's 80 is way too high, Denmark has only got 5! How about matching Denmark and going with 5. Keep the rest of the information the same except for the oob. Change the RUS to BYE. If you don't Byelorus will start with the same amount of troops in the same places as Russia! Save and close this document.
Bringing your Country into Existence
Now comes the fun part. Making your country exist! Go into the history folder again and open up the province folder. Find the category your country falls in, Byelorus would be in Soviet. It is recommended that you keep a list of Province ID's up in your web browser for this. Find any province that you want Byelorus to control at the start of the game or potentially own upon being released by Russia or have cores for. Open it up. (Byelorus' modern day borders are 936 to 939 - but you can modify them however you like. Inside you will find just a short block of text. Let's go with 936 - Grodno. Underneath the "add_core = POL" type "add_core = BYE" Byelorus now has a core in Grodno. If you want Byelorus to be releasable by Russia, just save and close the file.
If you want it to exist on the starting map of the grand campaign, then change the owner and controller from RUS to BYE. Save and close the document and move to the next one. Repeat. Congrats, using this information you should now be able to modify borders at the game start and add cores to provinces! Woo!
Getting a Flag
Flags are in the folder "flags" which is in the "gfx" folder. If you take a look, they are all 93 wide and 64 tall and in the .tga format. You need a program to do this, I recommend paint.net. Install the program and create a new document with the dimensions above. Now pick out a flag for Byelorus, I went with the white red white horizontal tricolor. Find an image on the internet and copy paste it into the program. Resize the image so it entirely fits in the canvas, do not resize the canvas to match the image. Now save it as a .tga with the name BYE. If you want to make different flags for different government types, you can! For the communist Byelorus, why not pick out the flag of the Byelorussian SSR and use that? Simply save it as BYE_communist with the correct dimensions and format! Move the .tga files to the flags folder and just leave them there.
Making your Country... Presentable
If you were to load up Victoria 2 right now, your country would be fully accessible. However, the name of your country would be whatever you made the tag. Try it. If it was releasable start a campaign as Russia. You do have the option to release Byelorus, however the name was BYE. Also, look at the region of Brest or Lida. Because it is split between Russian Brest and... BYE_ADJ Brest... that doesn't look right at all. Quit the game and go back to the files. Search the entire Victoria 2 folder for a file named "text.csv" and open it. It's comma delimited so make sure to maintain all formatting.
Ctrl-F and type in any tag you know to find the section where country names are defined. Insert a new line and copy/paste another so you don't have to meticulously type in semicolon formatting. The format (in Notepad) is as follows: tag;name(English);name(French);name(German);;name(Spanish);;;;;;;;;x,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Let's enter in: BYE;Byelorus;Byelorussie;Weissrusland,Belarussio;;;;;;;;;x,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
You don't have to get the foreign names correct. Now Ctrl-F again to find where you see the list of countries names with _ADJ following them. This is where the adjective for countries shows up. How does the game know to use "Russian" for all things defined by Russia? How is the part of Budjak owned by Russia called "Russian Budjak?" Because of this little line here. Follow the instructions listed above to modify a line for Byelorussian. And once you save this file, the game is completely playable without looking ugly. There is more you can do, but that is beyond this guide.