Entities.h :

#include "Map.h"
#include "TextureManager.h"
#include "Components.h"
#include "ECS.h"
#include "Vector2D.h"
#include "Collision.h"
#include "AnimateComponent.h"

extern Manager t_manager;
extern Entity& t_sky(t_manager.addEntity());

Entities.cpp :

#include "Entities.h"
void Entities::initent()
{
  t_sky.addComponent<TransformComponent>(0, 0, 640, 800, 1);
}

game.cpp :

#include "Entities.h"
Manager manager = t_manager;
Entity& sky(manager.addEntity());
void Game::init(const char *title,int xpos,int ypos,int width,int height,bool fullscreen)
{
    manager = t_manager;
    sky = t_sky;
}

and I get the Error:
LNK2005 “class Entity & t_sky” (?t_sky@@3AEAVEntity@@EA) already defined in Entities.obj

I have tried changing the files I include in each file but nothing seems to work.

Thank you in advance.