This document provides reference documentation for Millennium Dawn’s unique systems, including custom modifiers, scripted effects, and how-to guides for common modding tasks.

Note: This is not fully up-to-date. For the latest systems, check the codebase directly.

Quick Reference

Custom Modifier Categories

• Economic Modifiers - Money, taxes, productivity, trade
• Law Modifiers - Government spending, law costs
• Migration Modifiers - Population migration
• Influence Modifiers - Foreign influence mechanics
• Energy Modifiers - Power generation and consumption
• Political Modifiers - Party popularity mechanics
• Counter-Terror Modifiers - Counter-terrorism
• Missile & Space Modifiers - Missile/satellite production
• Nation-Specific Modifiers - Country unique modifiers

Scripted Effects Categories

• Building Effects - Add buildings with costs
• Economic Effects - Treasury, debt, productivity
• Internal Faction Effects - Faction opinions
• Influence Effects - Influence actions
• Political Effects - Party management
• Special System Effects - EU, Energy, Counter-Terror, Cartels

How-To Guides

• Add Subideology Parties
• Historical Events
• Variables
• Energy Configuration
• Unique Terrain Photos

Modifiers

Modifiers in Millennium Dawn follow standard HOI4 syntax but include many unique economic, political, and energy systems.

Economic Modifiers

These modifiers affect the economy, taxes, trade, and productivity.

General Economic

Exports & Resources

Industry Productivity

Industry Income Taxes

Campaign Costs

Investment Modifiers

Workforce & Labor

Upgrade & Special Costs

Education

Law Modifiers

These modify political power costs for changing government laws.

Migration Modifiers

These affect population migration.

Influence Modifiers

These affect the foreign influence system.

Energy Modifiers

These control power generation and consumption.

General Energy

Population Energy

Fossil Fuels

Nuclear Energy

Building Energy Use

Renewable Infrastructure

Battery & Storage

Political Modifiers

These affect internal politics.

Counter-Terror Modifiers

These affect the counter-terrorism system.

Missile & Space Modifiers

These affect missile and satellite production.

Nation-Specific Modifiers

Czech Republic

Italy

Scripted Effects

All scripted effects automatically generate tooltips. Do not add extra localization for these.

Building Effects

Location: common/scripted_effects/00_scripted_effects.txt

Buildings can be added using state scope or random scope:

State Scope (Predefined State)

117 = {
    one_state_industrial_complex = yes
}

Random Scope (Any Owned State)

one_random_industrial_complex = yes
two_random_industrial_complex = yes
three_random_industrial_complex = yes
four_random_industrial_complex = yes

Available Building Effects

Building Costs (State-Level)

The cost implies the INCLUSION of a building slot. A single building slot is $1.00 so if you want to give a Civilian Industry it’s $6.50 without a building slot.

Economic Effects

Treasury Management

# Modify treasury
set_temp_variable = { treasury_change = -10.00 }
modify_treasury_effect = yes

# Preset expenditures
small_expenditure = yes
medium_expenditure = yes
large_expenditure = yes

Debt Management

set_temp_variable = { debt_change = 0.1 }
modify_debt_effect = yes

Productivity

# Adjust productivity (flat value)
set_temp_variable = { temp_productivity_change = 0.025 }
flat_productivity_change_effect = yes

Economic Cycles

increase_economic_growth = yes
decrease_economic_growth = yes
depression = yes
recession = yes
stagnation = yes
stable_growth = yes
fast_growth = yes
economic_boom = yes

Government Spending Laws

# Bureaucracy
increase_centralization = yes
decrease_centralization = yes

# Social Spending
increase_social_spending = yes
decrease_social_spending = yes

# Education
increase_education_budget = yes
decrease_education_budget = yes

# Healthcare
increase_healthcare_budget = yes
decrease_healthcare_budget = yes

# Policing
increase_policing_budget = yes
decrease_policing_budget = yes

# Trade Law
increase_exports = yes
decrease_exports = yes

# Military Spending
increase_military_spending = yes
decrease_military_spending = yes

Internal Faction Effects

Changing Faction Opinions

set_temp_variable = { temp_opinion = 5 }
change_small_medium_business_owners_opinion = yes

Available Faction Effects

Influence Effects

Basic Influence

# Domestic influence
set_temp_variable = { percent_change = 10 }
change_domestic_influence_percentage = yes

# General influence (requires target)
set_temp_variable = { percent_change = 5 }
set_temp_variable = { tag_index = ROOT }
set_temp_variable = { influence_target = GER }
change_influence_percentage = yes

Index-Based Influence

set_temp_variable = { percent_change = 5 }
set_temp_variable = { influencer_index = 0 }
change_current_influencer_index_percentage = yes

Political Effects

Party Popularity

# Set party index (0-23) and change popularity
set_temp_variable = { party_index = 2 }
set_temp_variable = { party_popularity_increase = 0.10 }  # 10% = 0.10
add_relative_party_popularity = yes

# Or set to ruling party automatically
set_party_index_to_ruling_party = yes

Ruling Party Changes

# Set ruling party
set_temp_variable = { rul_party_temp = 20 }
change_ruling_party_effect = yes
set_politics = {
    ruling_party = nationalist
    elections_allowed = no
}

Coalition Management

# Add to coalition
set_temp_variable = { add_col_one = 5 }
add_coalition_members_effect = yes

# Remove from coalition
set_temp_variable = { remove_col_one = 5 }
remove_coalition_members_effect = yes

Ban/Allow Parties

# Ban party
set_temp_variable = { party_index = 1 }
ban_party_scripted_call = yes

# Allow party
set_temp_variable = { party_index = 1 }
unban_party_scripted_call = yes

Special System Effects

Euroscepticism (EU)

# Single country
set_temp_variable = { modify_eurosceptic = 0.05 }
set_temp_variable = { modify_eurosceptic_target = GER }
eurosceptic_change = yes

# All EU members
set_temp_variable = { modify_eurosceptic = -0.05 }
EU_eurosceptic_change = yes

Energy Systems

# Build enrichment facilities (cost: 25.00 each)
set_temp_variable = { temp_change = 2 }
build_enrichment_facilities_effect = yes

# Build battery parks (cost: 100.00 each)
set_temp_variable = { temp_change = 2 }
build_battery_park_effect = yes

Cartel Effects

Handles cartel strength and political influence changes.

# Modify cartel variables
set_temp_variable = { cart_strength_change = 2 }
set_temp_variable = { cart_influence_change = 2 }
modify_cartel_variables_effect = yes

How-To Guides

Adding Subideology Parties

Adding a new party requires edits to four files. Follow the steps below in order.

Step 1 — Choose a Slot

Consult the Subideology Slots table below to pick the subideology key and its index for the ideology group your party belongs to. Note both — you will need the key for localisation and the index for the history file.

Step 2 — Add Localisation

In localisation/english/MD_subideology_parties_l_english.yml, add three entries for the party using the format below:

TAG.subideology: "£TAG_icon_name (ABBRV) - Party Name"
TAG.subideology_icon: "£TAG_icon_name"
TAG.subideology_desc: "(Dominant Ideology) - Party Name (Native name, ABBRV)\n\nDescription"

If the party changes over time (e.g. a coalition partner becomes dominant), add _alt variants:

TAG.subideology_alt: "£TAG_icon_name_alt (ABBRV) - Alternate Party Name"
TAG.subideology_icon_alt: "£TAG_icon_name_alt"
TAG.subideology_desc_alt: "(Dominant Ideology) - Alternate Party Name (Native name, ABBRV)\n\nDescription"

Step 3 — Register the Icon

a) Add the GFX entry to interface/MD_parties_icons.gfx, keeping entries sorted alphabetically by tag:

spriteType = {
	name = "GFX_TAG_icon_name"
	texturefile = "gfx/texticons/parties_icons/country_name_lowercase/TAG_icon_name.dds"
	legacy_lazy_load = no
}

The name value must match the icon referenced in localisation (without the £ prefix, prefixed with GFX_).

b) Place the DDS file at gfx/texticons/parties_icons/{country_name_lowercase}/TAG_icon_name.dds. Party icon DDS files are typically 20×20 px text icons.

Step 4 — Set Starting Popularity

In history/countries/TAG - Country.txt, set the party’s starting popularity using its slot index. A comment with the party abbreviation is required:

set_variable = { party_pop_array^N = 0.15 } # Party Abbreviation

Where N is the slot index from the slots table. Only set slots for parties that actually exist in the country — leave unused slots unset (they default to 0).

If the party holds government or is a coalition partner at game start, also add:

add_to_array = { ruling_party = N }          # if this party governs alone or leads the coalition
add_to_array = { gov_coalition_array = N }   # if this party is a junior coalition partner

For countries with elections, set the most recent election results separately:

set_variable = { party_pop_elect_array^N = 0.15 } # Party Abbreviation - election result

Step 5 — Add Leaders (Optional)

If the country has scripted leader rotation, add the leader’s create_country_leader block inside the appropriate if = { limit = { has_country_flag = set_subideology } } block in common/scripted_effects/TAG_political_leaders.txt. Create the file if it doesn’t yet exist for this tag.

Subideology Slots

Historical Events (ETD System)

Events should use the yearly effects system in common/scripted_effects/00_yearly_effects.txt:

# First year events
MD_event_on_startup_events = {
    CAM = { country_event = { id = Cameroon.1 days = 50 random_days = 50 } }
}

# Specific year events
trigger_year_2067_events = {
    USA = { country_event = { id = collapse_event.1 days = 30 random_days = 336 } }
}

Variable Basics

# Set variable
set_variable = { var = example_var value = 1 }

# Add to variable
add_to_variable = { var = example_var value = 1 }

# Set bounds
set_variable = { var = example_var value = 50 max = 100 min = 0 }

Energy Configuration

Hydroelectric/Geothermal

set_variable = { hydroelectric_energy_production_var = 5.636 }
set_variable = { hydroelectric_energy_storage_var = 300 }
add_dynamic_modifier = { modifier = hydroelectric_infrastructure_in_state }

Renewable Capacity (from Global Wind Atlas)

# Capacity factor = (Atlas value) - 0.25
set_variable = { state_renewable_capacity_factor_modifier_var = 0.55 }

Unique Terrain Photos

Adds custom terrain photos to specific provinces.

Step 1: Create Image

• Size: 413x70px
• Format: DDS
• Location: gfx/interface/terrain/

Step 2: Register in GFX File

File: interface/MD_terrain_cities.gfx

spriteType = {
    name = "GFX_terrain_brussels"
    textureFile = "gfx/interface/terrain/your_image.dds"
}

Step 3: Create GUI Icon

File: interface/countrystateview.gui

iconType = {
    name = "terrain_brussels_icon"
    spriteType = "GFX_terrain_brussels"
    alwaystransparent = yes
}

Step 4: Create Empty Modifier

File: common/modifiers/01_province_modifiers.txt

terrain_brussels = { }

Step 5: Add to Startup Effects

File: common/scripted_effects/00_startup_effects.txt

# State ID 50, province ID 516
50 = {
    add_province_modifier = {
        static_modifiers = { terrain_brussels }
        province = { id = 516 }
    }
}

Tip: Use Tdebug console command in-game to find state and province IDs.

Additional Resources

• Discord: @AngriestBird for questions
• Error Codes: See docs/dev-resources/error-debug-codes.md
• Focus Trees: See .cursor/.ai-guides/code_styling.md