We present a divide-and-conquer method, called DiConic, for automatic addition of failsafe fault-tolerance to distributed programs, where a failsafe program guarantees to meet its safety specification even when faults occur. Specifically, instead of adding fault-tolerance to a program as a whole, we separately revise program actions so that the entire program becomes failsafe fault-tolerant. Our DiConic algorithm has the potential to utilize the processing power of a large number of machines working in parallel, thereby enabling automatic addition of failsafe fault-tolerance to distributed programs with a large number of processes. We formulate our DiConic synthesis algorithm in terms of the satisfiability problem and demonstrate our approach for the classic Byzantine Generals problem and an industrial application.