Complex sentence: In a little over two weeks, the Red Army had advanced 300 miles from the Vistula to the Oder, apparently within striking distance of Berlin, though stubborn German resistance delayed the final offensive till April.
Split into simpler sentences: In a little over two weeks, the Red Army had advanced 300 miles from the Vistula to the Oder, apparently within striking distance of Berlin. But stubborn German resistance delayed the final offensive till April.