diff --git a/src/fheroes2/castle/castle.cpp b/src/fheroes2/castle/castle.cpp
index 431ac749182..f8f3cbfda9d 100644
--- a/src/fheroes2/castle/castle.cpp
+++ b/src/fheroes2/castle/castle.cpp
@@ -2414,15 +2414,12 @@ void Castle::ActionAfterBattle( bool attacker_wins )
 
 Castle * VecCastles::GetFirstCastle() const
 {
-    const_iterator it = std::find_if( begin(), end(), []( const Castle * castle ) { return castle->isCastle(); } );
-    return end() != it ? *it : nullptr;
-}
+    const_iterator iter = std::find_if( begin(), end(), []( const Castle * castle ) { return castle->isCastle(); } );
+    if ( iter == end() ) {
+        return nullptr;
+    }
 
-void VecCastles::ChangeColors( int col1, int col2 )
-{
-    for ( iterator it = begin(); it != end(); ++it )
-        if ( ( *it )->GetColor() == col1 )
-            ( *it )->ChangeColor( col2 );
+    return *iter;
 }
 
 AllCastles::AllCastles()
diff --git a/src/fheroes2/castle/castle.h b/src/fheroes2/castle/castle.h
index 38e94737af7..c163b0c64d7 100644
--- a/src/fheroes2/castle/castle.h
+++ b/src/fheroes2/castle/castle.h
@@ -413,9 +413,14 @@ namespace CastleDialog
 
 struct VecCastles : public std::vector<Castle *>
 {
-    Castle * GetFirstCastle() const;
+    VecCastles() = default;
+    VecCastles( const VecCastles & ) = delete;
+
+    ~VecCastles() = default;
 
-    void ChangeColors( int, int );
+    VecCastles & operator=( const VecCastles & ) = delete;
+
+    Castle * GetFirstCastle() const;
 };
 
 class AllCastles
diff --git a/src/fheroes2/game/difficulty.cpp b/src/fheroes2/game/difficulty.cpp
index f3f3e06a504..ca56678ec4e 100644
--- a/src/fheroes2/game/difficulty.cpp
+++ b/src/fheroes2/game/difficulty.cpp
@@ -26,9 +26,11 @@
 #include <cassert>
 #include <vector>
 
+#include "kingdom.h"
 #include "profit.h"
 #include "race.h"
 #include "translations.h"
+#include "world.h"
 
 std::string Difficulty::String( int difficulty )
 {
@@ -68,8 +70,10 @@ int Difficulty::GetScoutingBonusForAI( int difficulty )
     return 0;
 }
 
-Funds Difficulty::getResourceIncomeBonusForAI( const int difficulty, const VecCastles & castles )
+Funds Difficulty::getResourceIncomeBonusForAI( const int difficulty, const Kingdom & kingdom )
 {
+    assert( kingdom.isControlAI() );
+
     const auto getIncomeFromSetsOfResourceMines = []( const int resourceTypes, const uint32_t numOfSets ) {
         Funds result;
 
@@ -78,16 +82,28 @@ Funds Difficulty::getResourceIncomeBonusForAI( const int difficulty, const VecCa
         return result * numOfSets;
     };
 
-    const auto getBonusForCastles = [&castles]() {
+    const auto getBonusForCastles = [kingdomColor = kingdom.GetColor(), &kingdomCastles = kingdom.GetCastles()]() {
         Funds result;
 
-        for ( const Castle * castle : castles ) {
+        const bool kingdomHasMarketplace = std::any_of( kingdomCastles.begin(), kingdomCastles.end(), []( const Castle * castle ) {
+            assert( castle != nullptr );
+
+            return castle->isBuild( BUILD_MARKETPLACE );
+        } );
+
+        // Additional rare resources for hiring units from higher-level dwellings can only be provided if the kingdom already has some source of those resources - either
+        // through trade or through mining
+        const auto canKingdomGetResource = [kingdomColor, kingdomHasMarketplace]( const int resourceType ) {
+            return ( kingdomHasMarketplace || world.CountCapturedMines( resourceType, kingdomColor ) > 0 );
+        };
+
+        for ( const Castle * castle : kingdomCastles ) {
             assert( castle != nullptr );
 
             // AI at higher difficulty levels should be able to fully redeem the weekly unit growth in its castles
             result += ProfitConditions::FromMine( Resource::GOLD );
 
-            // Offer additional resources only if there are higher-level dwellings in the castle to avoid distortions in the castle's development rate
+            // Provide additional resources only if there are higher-level dwellings in the castle to avoid distortions in the castle's development rate
             if ( !castle->isBuild( DWELLING_MONSTER6 ) ) {
                 continue;
             }
@@ -98,18 +114,26 @@ Funds Difficulty::getResourceIncomeBonusForAI( const int difficulty, const VecCa
                 // Rare resources are not required to hire maximum-level units in these castles
                 break;
             case Race::BARB:
-                result += ProfitConditions::FromMine( Resource::CRYSTAL );
+                if ( canKingdomGetResource( Resource::CRYSTAL ) ) {
+                    result += ProfitConditions::FromMine( Resource::CRYSTAL );
+                }
                 break;
             case Race::SORC:
-                result += ProfitConditions::FromMine( Resource::MERCURY );
+                if ( canKingdomGetResource( Resource::MERCURY ) ) {
+                    result += ProfitConditions::FromMine( Resource::MERCURY );
+                }
                 break;
             case Race::WRLK:
-                result += ProfitConditions::FromMine( Resource::SULFUR );
+                if ( canKingdomGetResource( Resource::SULFUR ) ) {
+                    result += ProfitConditions::FromMine( Resource::SULFUR );
+                }
                 // The maximum level units in this castle are more expensive than in others
                 result += ProfitConditions::FromMine( Resource::GOLD );
                 break;
             case Race::WZRD:
-                result += ProfitConditions::FromMine( Resource::GEMS );
+                if ( canKingdomGetResource( Resource::GEMS ) ) {
+                    result += ProfitConditions::FromMine( Resource::GEMS );
+                }
                 // The maximum level units in this castle are more expensive than in others
                 result += ProfitConditions::FromMine( Resource::GOLD );
                 break;
diff --git a/src/fheroes2/game/difficulty.h b/src/fheroes2/game/difficulty.h
index 3704c2b0974..66043766054 100644
--- a/src/fheroes2/game/difficulty.h
+++ b/src/fheroes2/game/difficulty.h
@@ -47,7 +47,7 @@ namespace Difficulty
     int GetScoutingBonusForAI( int difficulty );
 
     // Returns an extra resource bonus for AI based on difficulty level.
-    Funds getResourceIncomeBonusForAI( const int difficulty, const VecCastles & castles );
+    Funds getResourceIncomeBonusForAI( const int difficulty, const Kingdom & kingdom );
 
     // Returns an extra gold bonus modifier for AI based on difficulty level. This modifier is applied after applying the resource income bonus.
     double getGoldIncomeBonusForAI( const int difficulty );
diff --git a/src/fheroes2/kingdom/kingdom.cpp b/src/fheroes2/kingdom/kingdom.cpp
index c7d2e000242..27f25f88611 100644
--- a/src/fheroes2/kingdom/kingdom.cpp
+++ b/src/fheroes2/kingdom/kingdom.cpp
@@ -178,25 +178,30 @@ bool Kingdom::isPlay() const
 
 void Kingdom::LossPostActions()
 {
-    if ( isPlay() ) {
-        Players::SetPlayerInGame( color, false );
+    if ( !isPlay() ) {
+        return;
+    }
 
-        // Heroes::Dismiss() calls Kingdom::RemoveHero(), which eventually calls heroes.erase()
-        while ( !heroes.empty() ) {
-            Heroes * hero = heroes.back();
+    Players::SetPlayerInGame( color, false );
 
-            assert( hero->GetColor() == GetColor() );
+    // Heroes::Dismiss() calls Kingdom::RemoveHero(), which eventually calls heroes.erase()
+    while ( !heroes.empty() ) {
+        Heroes * hero = heroes.back();
 
-            hero->Dismiss( static_cast<int>( Battle::RESULT_LOSS ) );
-        }
+        assert( hero->GetColor() == GetColor() );
 
-        if ( !castles.empty() ) {
-            castles.ChangeColors( GetColor(), Color::NONE );
-            castles.clear();
-        }
+        hero->Dismiss( static_cast<int>( Battle::RESULT_LOSS ) );
+    }
+
+    for ( Castle * castle : castles ) {
+        assert( castle != nullptr && castle->GetColor() == GetColor() );
 
-        world.ResetCapturedObjects( GetColor() );
+        castle->ChangeColor( Color::NONE );
     }
+
+    castles.clear();
+
+    world.ResetCapturedObjects( GetColor() );
 }
 
 void Kingdom::ActionBeforeTurn()
@@ -598,20 +603,22 @@ bool Kingdom::AllowRecruitHero( bool check_payment ) const
 
 void Kingdom::ApplyPlayWithStartingHero()
 {
-    if ( !isPlay() || castles.empty() )
+    if ( !isPlay() || castles.empty() ) {
         return;
+    }
 
     bool foundHeroes = false;
 
     for ( const Castle * castle : castles ) {
-        if ( castle == nullptr )
+        if ( castle == nullptr ) {
             continue;
+        }
 
-        // check manual set hero (castle position + point(0, 1))?
+        // Check if there is a hero placed by the map creator near the castle entrance (castle position + point(0, 1))
         const fheroes2::Point & cp = castle->GetCenter();
         Heroes * hero = world.GetTiles( cp.x, cp.y + 1 ).getHero();
 
-        // and move manual set hero to castle
+        // If there is, move it to the castle
         if ( hero && hero->GetColor() == GetColor() ) {
             const bool patrol = hero->Modes( Heroes::PATROL );
             if ( hero->isValid() ) {
@@ -626,19 +633,21 @@ void Kingdom::ApplyPlayWithStartingHero()
                 hero->SetModes( Heroes::PATROL );
                 hero->SetPatrolCenter( cp );
             }
+
             foundHeroes = true;
         }
     }
 
     if ( !foundHeroes && Settings::Get().getCurrentMapInfo().startWithHeroInEachCastle ) {
-        // get first castle
         const Castle * first = castles.GetFirstCastle();
-        if ( nullptr == first )
+        if ( first == nullptr ) {
             first = castles.front();
+        }
 
         Heroes * hero = world.GetHeroForHire( first->GetRace() );
-        if ( hero && AllowRecruitHero( false ) )
+        if ( hero && AllowRecruitHero( false ) ) {
             hero->Recruit( *first );
+        }
     }
 }
 
@@ -707,7 +716,7 @@ Funds Kingdom::GetIncome( int type /* = INCOME_ALL */ ) const
     }
 
     if ( isControlAI() ) {
-        const Funds incomeBonus = Difficulty::getResourceIncomeBonusForAI( Game::getDifficulty(), GetCastles() );
+        const Funds incomeBonus = Difficulty::getResourceIncomeBonusForAI( Game::getDifficulty(), *this );
         if ( incomeBonus.GetValidItemsCount() != 0 ) {
             DEBUG_LOG( DBG_AI, DBG_TRACE, "AI bonus to the resource income has been applied to " << Color::String( color ) << ": " << incomeBonus.String() );