Final answer:
Roon and Moltke reproached Bismarck for his resignation threats because his Realpolitik and diplomacy were crucial for Prussia's success and unification of Germany under Prussian dominance.
Step-by-step explanation:
Roon and Moltke reproached Bismarck for threatening to resign because they realized that Bismarck's strategic Realpolitik and his skills in managing international relations were crucial for advancing Prussia's power in Europe. Bismarck had engineered several key victories, including manipulating political situations to unify Germany under Prussian rule. His efforts culminated in the Franco-Prussian War, which not only discredited Napoleon III but also paved the way for the proclamation of the German Empire in 1871. Bismarck’s ability to not only manage domestic policy but also navigate the complex landscape of European alliances was instrumental to Prussia's success. Additionally, Bismarck’s Realpolitik was vital for manipulating these events to Prussia's advantage. Therefore, Roon and Moltke saw Bismarck's potential resignation as a threat to Prussia’s position and future ambitions.