The United States also tried to invade Canada.

Semiconductor lasers have a very high gain and the cleaved facets of the chip itself actually act as mirrors to reflect light within the cavity. In some cases, the facets are also coated with a thin-film. Reflecting laser light back into the cavity (after it's emitted) creates an unstable oscillator. Generally avoided when performing science as it causes erratic light output. I didn't RTFA, but I have experience working with lasers.