Complex sentence: The real issue, however, was that Rutskoy sided with the parliament during the Russian constitutional crisis of 1993, which was triggered when Yeltsin tried to dissolve the parliament on September 21, the parliament responded by declaring Yeltsin's presidency unconstitutional and appointing Rutskoy acting president.
Split into simpler sentences: The real issue, however, was that Rutskoy sided with the parliament during the Russian constitutional crisis of 1993, which was triggered when Yeltsin tried to dissolve the parliament on September 21. Parliament members responded by declaring Yeltsin's presidency unconstitutional and appointing Rutskoy acting president.