Space Pirate: Captain Harlock is based on the manga/anime of the same name created in 1977 by legendary mangaka Leiji Matsumoto.
The original Harlock anime series aired in 1978-79, and like most of Matsumoto's works, revolved around one character fighting against human apathy, selfishness and laziness.
In Matsumoto's series Galaxy Express 999, for example, protagonist Tetsuro takes a train to reach a planet where he can get a robotic body, and so take revenge against the cyborg aristocrat who killed his mother for sport. In Space Battleship Yamato, the crew is on a desperate mission to a faraway galaxy to obtain technology that will fix Earth's climate troubles.
In the original Harlock series, Earth is under the control of aliens, and the main man has to save it. Harlock becomes a pirate to foil the aliens' plans, and at the same time and hold up a mirror to the government's failure to stand up for its people.
The new movie reflects modern themes while keeping the original story idea of alien control and inept rule by a corrupt government. Some might say that situation is not entirely unfamiliar to those of us watching here...