Sure! Here's a simple gang war game implemented as a single HTML file using JavaScript and enclosed within script tags:
Gang War Game
In this game, three gangs (Gang A, Gang B, and Gang C) are displayed on a canvas using their respective icons. When the user clicks on a gang's icon, an alert is shown indicating which gang has been chosen.
Please note that this is a very basic implementation of a gang war game and can be expanded upon with more features and gameplay mechanics based on your requirements.