{} literally means "lots of difficulties". There are a few different ways of producing a potential "antonym", depending on what kind of meaning you're looking for. {} literally means "lots of happinesses / good fortune", and this is often seen as the closest to an antonym. Other possibilities include {} "no difficulty", as noted by l'électeur earlier, or {} "minor difficulty, not much of a difficulty", as noted by in a comment above. Another possible antonym would conceivably be {} "few difficulties", but this seems to be a very rare word, appearing in only a few books, and this does not appear to be recognized as a valid Japanese word by most dictionaries.
All that said, simply using the antonym supplied by the thesaurus would seem to produce the desired reversal in meaning:
* → "European expansion off to a rocky start"
* → "European expansion off to an auspicious start"