Complex sentence: The planned peace conference never took place and the border has remained where it was provisionally placed in 1945, confirmed in the treaties that Poland signed with West Germany in 1970 and with unified Germany in 1990.
Split into simpler sentences: The planned peace conference never took place and the border has remained where it was provisionally placed in 1945. It was confirmed in the treaties that Poland signed with West Germany in 1970 and with the unified Germany in 1990.