The Lutheran-Reformed relationship has often been difficult. Lutherans and Calvinists debated theology so fiercely in the 16th Century that each side condemned teachings of the other. In the mid-19th Century there was a large immigration of Lutherans from Germany -- people persecuted for their opposition to the King's "Prussian Union" of Lutherans and Reformed into a single Evangelical (Protestant) Church. Their theological descendants in the US are Lutherans of the Missouri Synod, the Wisconsin Synod, and the mid-west "German" branches of the ELCA.
Today Lutheran and Reformed Churches are in full communion in Germany and other parts of Europe. Here in the United States, the ELCA and the 3 Reformed church bodies below voted in 1997 to establish full communion. So, it seems that -- 150 years later -- the King of Prussia has nearly succeeded.
Presbyterian Church (U.S.A.)