FLOURISH. Let us look at the meanings of the given options :WEAKEN: make or become weaker in power, resolve, or physical STRENGTHEND: reach a point and go no further; finishstrive: make great EFFORTS to achieve or obtain somethingflourish: develop rapidly and SUCCESSFULLY The passage is about conditions that favour the growth of democracy and dictatorship. The most suitable option here is 'flourish' as 'growth' of democracy is concerned.