The phrase "decade after decade" means that something has been happening consistently and repeatedly for multiple periods of ten years. Full definition
No business does business the same way successfully for decade after decade. (businessoffashion.com)
When you have a poverty imposed on a country decade after decade, somebody is benefiting from all this and people are saying isn't it too bad that economies are getting poor. (michael-hudson.com)
We've seen clearly what happens when decade after decade adults fail to reach their nutritional quota. (flippingfifty.com)