To quickly defeat Poland, France and Denmark within a couple minutes, you must first create plenty of bombers and at least three artillery cannons. Use the artillery to destroy your Capital, then you can send your bombers to Poland, France and Denmark. Destroy their Capitals, then select one of your citizens to create a Capital on the same location in Poland. Immediately delete the Capital and use a citizen to create a Capital in France or Denmark. Repeat the process. The defeated cities will not attack your base. The only enemy will be Great Britain. Make sure to create plenty of AA to protect your Airbase and Research Center. You can then clean up the path to each of the destroyed Capitals to create a Capital and Town Centers in Poland, France and Denmark.