Complex sentence: The Portuguese forces were able to stop the local militias in certain cities, including Salvador, Montevideo and São Luís, but failed to defeat the militias in most of the other cities and proved ineffective against the guerrilla forces in the rural areas of the country.
Split into simpler sentences: The Portuguese forces were able to stop the local militias in certain cities, including Salvador, Montevideo and São Luís. However, they failed to defeat the militias in most of the other cities and proved ineffective against the guerrilla forces in the rural areas of the country.