The best work in English on Germany I have in my library is Gordon Craig's The Germans. After a short chapter entitled Historical Perspectives, Craig divides his work topically: Politics in a New Key, Hitler and the New Generation, Religion, Money, Germans and Jews, Women, Professors and Students, Romantics, Literature and Society, Soldiers, Berlin, Democracy and Nationalism, and The Awful German Language, It concentrates, as these titles suggest, on the 20th century, especially after 1945. Although I have not seen it, Craig's Germany, 1866 to 1945, would cover most of the rest of your inquiry. I have followed Craig for decades in his voluminous reporting and essays on Germany until his death in 2005. Truly the - at least at the top of a short list of the - most prolific and insightful of historians of Germany in the English language, or perhaps any language. The New York Times and the New York Review of Books will have volumes of Craig's pieces on Germany. For English language histories of "Germany" prior to Der Deutsche Krieg od. Der Preußisch-Deutscher Krieg, I cannot help.
There is also Tony Judt's Postwar, A History of Europe Since 1945, for the larger context, and in earlier chapters, perhaps the most moving description of the immediate aftermath of WWII in Germany.
You might also wish to peruse Wulf Kansteiner's In Pursuit of German Memory, History, Television and Politics after Auschwitz, for assignable specific postwar topics.
A translation of about 100 pages, beginning at page 71, of Michael Freund's Deutsche Geschichte, would fill in the 19th century gap. A readable concise history "Von den Anfängen bis zur Gegenwart" (1969). A project for your students. For extra credit, they can translate the first 70. :-)