Here is a list of themes by year.
Current Theme (2018): Conflict and Compromise in History
2019: Triumph and Tragedy in History
2020:
2017 - Taking a Stand in History
2016 - Exploration, Encounter, Exchange in History
2015 - Leadership and Legacy in History
2014 - Rights and Responsibilities in History
2013 - Turning Points in History: People, Ideas, Events
2012 - Revolution, Reaction, Reform in History
2011 - Debate and Diplomacy in History: Successes, Failures, Consequences
2010 - Innovation in History: Impact and Change
2009 - The Individual in History: Actions and Legacies
2008 - Conflict and Compromise in History
2007 - Triumph and Tragedy in History
2006 - Taking a Stand in History
2005 - Communication in History: The Key to Understanding
2004 - Exploration, Encounter, Exchange in History
2003 - Rights and Responsibilities in History
2002 - Revolution, Reaction, Reform in History
2001 - Frontiers in History
2000 - Turning Points in History
And more past themes from National History Day