Final answer:
The Kaiser supported Austria-Hungary with a "blank check" of military backing, which encouraged Austria-Hungary to aggressively confront Serbia, leading to WWI after interlocking alliances were activated.
Step-by-step explanation:
The Kaiser, or German Emperor, advised the Czar of Russia regarding the Austro-Serbian incident that led to the outbreak of World War I. Germany, in its commitment to support its ally Austria-Hungary, issued a "blank check", offering unconditional military support. This emboldened Austria-Hungary to present a harsh ultimatum to Serbia, leading to its invasion after Serbia refused to meet all demands. The Kaiser's advice and Germany's backing effectively encouraged Austria-Hungary to take a hard line against Serbia, which was determined to maintain its independence despite agreeing to many concessions.
German leaders pushed for a declaration of war on Serbia by Austria-Hungary, as they believed their military and industrial strength would ensure a victory against Serbia and any allied forces. This set off a domino effect within the European alliance system, whereby Russia sided with Serbia, France with Russia, and Britain allied with France. The Austro-Serbian conflict, initially a regional dispute, quickly spiraled into a full-scale global conflict due to these interlocking alliances and the Kaiser's unwavering support for Austria-Hungary.