Sure! Here's a simple open-world war game implemented as a single HTML file, utilizing JavaScript for the game logic. This game is optimized for smartphone operation and utilizes pictograms for a better gaming experience. Please note that this is a basic implementation and can be further expanded upon to add more features and complexity.
To play the game, copy the code below and save it as a .html file. Then, open the saved file in a web browser on your smartphone.
In this game, you control the player character with arrow keys. The objective is to avoid colliding with the enemy character that moves randomly across the game area. If you collide with the enemy, you lose the game and it will reset.
Please note that this is a minimalistic implementation and can be enhanced with additional game mechanics, levels, scoring, visuals, and more.