Complex sentence: The Emancipation Oak, a national historical landmark was the catalyst for the 140th Year Anniversary Celebration of the Emancipation Proclamation and in 2004 the oak was named America's national tree.
Split into simpler sentences: The Emancipation Oak, a National Historical Landmark, was itself the catalyst for the 140th anniversary celebration of the Emancipation Proclamation. In fact, the following year, in 2004, the oak was named America's national tree.