Generate minecraft alike terrain

When I create a 3D space of cubes, unity gets stuck on starting because of the hard process. I was wondering how games like minecraft or ace of spades, make their games so smooth while generating thousands and thousands of blocks.

An example of code to spawn some blocks:

 for(int x = 0; x < 10; x++)
         {
             for(int z = 0; z < 10; z++)
             {
                 for(int y = 0; y < 10; y++)
                 {
                     position = new Vector3(x, y, z);
                     Block.PlaceAt(position);
                 }
             }
         }

As you can see, this generates 1000 cubes, but can't handle this process. How is this done properly? Do you know any guides/links for this?

Thanks