Article: Historians Luciano Petech and Sato Hisashi argue that the Ming upheld a "divide-and-rule" policy towards a weak and politically fragmented Tibet after the Sakya regime had fallen. Chan writes that this was perhaps the calculated strategy of the Yongle Emperor, as exclusive patronage to one Tibetan sect would have given it too much regional power. Sperling finds no textual evidence in either Chinese or Tibetan sources to support this thesis of Petech and Hisashi. Norbu asserts that their thesis is largely based on the list of Ming titles conferred on Tibetan lamas rather than "comparative analysis of developments in China and Tibet." Rossabi states that this theory "attributes too much influence to the Chinese," pointing out that Tibet was already politically divided when the Ming dynasty began. Rossabi also discounts the "divide-and-rule" theory on the grounds of the Yongle Emperor's failed attempt to build a strong relationship with the fifth Karmapa—one which he hoped would parallel Kublai Khan's earlier relationship with the Sakya Phagpa lama. Instead, the Yongle Emperor followed the Karmapa's advice of giving patronage to many different Tibetan lamas.

Now answer this question: When did the Ming hold the divide and rule policy?
after the Sakya regime had fallen