Dockless electric scooters first started appearing on US city streets in 2017, and since then have exploded in popularity across the world. Like ride-sharing, these compact two-wheelers were eagerly adopted by riders, kicking off what is seen as a revolution in micromobility. They can be a fun and easy way to make short trips, and startups like Bird and Lime are using that to raise huge amounts of cash. But critics complain they block sidewalks and cause injuries, and cities have struggled to manage their growth, which suggests that the scooter wars have only just begun.