Given the size and scope of what an Ultimate Genera game can coverl, I'd like to suggest the opening weeks of the WW1 on the Eastern Front, as the Russian's blundered into east Prussia and were caught at Tannenberg. It's a fantastic setting of foreboding forest, countless lakes, narrow corridors between them and sandy cliffs. All of the defining characteristics of WW1 combat (devastating artillery, surveillance balloons and planes, infantry entrenchment, blunted effectiveness of calvary) are present, without the limitation of long term fixed positions. The forces here were still mobile. I'd recommend to anyone to read Solzhenitsyn's August 1914 to grasp why this would be such an excellent fit!