Complex sentence: Brazil--which imported 80 percent of the oil it consumed--had been greatly affected by the 1973 oil crisis, an event which had a tremendously negative impact on Brazil's current account and posed a major threat against its fast growth during previous years.
Split into simpler sentences: Brazil--which imported 80 percent of the oil it consumed--had been greatly affected by the 1973 oil crisis. The crisis had a tremendously negative impact on Brazil's current account and posed a major threat against its fast growth during previous years.