You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Warsaw

Context:
Warsaw's mixture of architectural styles reflects the turbulent history of the city and country. During the Second World War, Warsaw was razed to the ground by bombing raids and planned destruction. After liberation, rebuilding began as in other cities of the communist-ruled PRL. Most of the historical buildings were thoroughly reconstructed. However, some of the buildings from the 19th century that had been preserved in reasonably reconstructible form were nonetheless eradicated in the 1950s and 1960s (e.g. Leopold Kronenberg Palace). Mass residential blocks were erected, with basic design typical of Eastern bloc countries.

Question:
When did Warsaw start to rebuild?

After liberation