Complex sentence: Spanish exploration of Brazil's interior preceded Portuguese exploration, beginning with Orellana's navigation of the Amazon River in 1542, the beginning of many explorations, especially in those areas that now are part of Brazil's periphery near Spanish speaking countries.
Split into simpler sentences: Spanish exploration of Brazil's interior preceded Portuguese exploration, beginning with Orellana's navigation of the Amazon River in 1542. This was the beginning of many explorations, especially in those areas that now are in present day Brazil, near Spanish speaking countries.