Complex sentence: Robert Goelet planned to develop his lot at neighboring 2--6 West 49th, but could not do so because Cromwell controlled a property easement over part of Goelet's land.
Split into simpler sentences: Robert Goelet planned to develop his lot at neighboring 2--6 West 49th. However, he could not develop the land because Cromwell controlled a property easement over part of Goelet's land.