Complex sentence: The Bulgarian behavior had also a long-term impact on the Russo-Bulgarian relations as together with the uncompromising Bulgarian position tο review the prewar agreement with Serbia during a second Russian initiative for arbitration between them, finally led Russia to cancel its alliance with Bulgaria.
Split into simpler sentences: The Bulgarian behavior had also a long-term impact on the Russo-Bulgarian relations. The uncompromising Bulgarian position tο review the pre-war agreement with Serbia during a second Russian initiative for arbitration between them finally led Russia to cancel its alliance with Bulgaria.