Ok, and is there a question??
The infinitive phrase in this sentence is to speak clearly, and it is used as a subject of the sentence. What/who is essential to being understood? To speak clearly.
<span>With the Republican cause all but lost, its leaders attempted to negotiate a peace, but Franco refused. On March 28, 1939, the victorious Nationalists entered Madrid in triumph, and the Spanish Civil War came to an end. Up to a million lives were lost in the conflict, the most devastating in Spanish history.</span>
