As part of a story idea, I'd like to create an alien civilization that colonized different solar systems in a manner similar to how European nations colonized other continents here on Earth. This civilization would have the technology to make travel between solar systems feasible, though certainly not without risk. At the same time, their political and economic systems resemble those prevalent in 16th century Europe. In particular, institutions such as democratic republics and corporations would be in their early stages while concepts like consumerism and environmentalism would be completely unheard of.
There are many works of fiction where alien civilizations have similar discrepancies in technological and social development. However, none of the works I'm familiar with providing a plausible explanation as to why; if any explanation is provided, it's due to some dramatic device or extenuating circumstances; I'd prefer an explanation that seems natural and logical.
The alien species needs to resemble humans in most respects, both physiological and psychological; humans would be able to interact and relate to them on a meaningful, personal level.
Any suggestions on plausible explanations? Are there any works that I could refer to for inspiration?
EDIT: To clarify, my chief concern is that I don't want this space faring civilization to have conceived of (or at least remember developing) many concepts that are essential to modern life. Here are some the concepts that I definitely don't want this alien civilization to be familiar with:
- Corporate person-hood: The idea that a business can be an entity separate from those operating it.
- Mass Marketing & Advertisement: The idea of promoting and selling a specific item to a broad national or global audience instead of catering to a niche market.
- Specialization: The idea that individuals learn very specific skills and work in professions that tackle very specific needs as well as the idea that individual businesses would only produce part of a final product or only play a limited role in providing a service.
- Automation: The idea that technology could be leveraged to perform tasks without direct interaction or oversight.
- Conservation & Sustainability: The idea that a civilization can consume resources at such a pace that it could exhaust them and that special measures are needed to prevent this.
Though the political and economic systems of the 16th century aren't necessarily inferior, I fail to see how they could support the sophisticated industrial complex needed to for our current space programs, let alone intergalactic travel. Even if the aliens eventually develop the necessary technologies, would they be able to put it to use? Also, how would the new opportunities and challenges associated with more sophisticated technology not inspire them to explore more modern concepts?
EDIT 2: Thank you everyone for your responses. I've selected rideoutcolin's answer because I feel it best addresses how to maintain technological progress without dramatically changing the social order.