The antonyms for the phrase "were foundation for" can indicate a lack of support, stability, or grounding. Antonyms such as instability, weakness, and fragility imply that there was no solid or secure starting point for something. The opposite of a foundation could also be the destruction or demolition of something previously established. Antonyms that signal such undoing include collapse, destruction, and demolition. In sum, the antonyms for "were foundation for" point to notions of uncertainty, disintegration, and dissolution, all of which undermine or remove the sense of firm grounding that a foundation provides.