You should take a listen to this interview with Dr. Scott Murray, currently the fifth vice-President of the Lutheran Church – MIssouri Synod (LC-MS). It is called Unionism, Syncretism, and Ecumenism, and it is an excellent introduction, both in terms of history and theology.
The only thing in the interview that may be potentially confusing to some is Murray’s mention of the “Kingdom of the Left”. This has nothing to do with the modern political left, but is simply the Lutheran term of designation for one of the two ways that God rules the world. God rules the world through His Church’s use of His Word and Sacraments – particularly through the free forgiveness, life, and salvation given in Jesus Christ – and He rules the world via sword-bearing rulers through the “natural law” in men’s consciences (and, originally, through God’s revealed law as well) – particularly through the binding powers of human reason and the force of law. This distinction arose in the 16th century, as Luther attempted to expand on and further clarify insights that St. Augustine made in his classic work, the City of God.