There was a spell of bad periods in the past, but now it's gone.
In the past there had been a spell of dreadful times, but that seems to be long gone.
ご質問ありがとうございます。
「spell of」は使いたいなら、「There was a spell of bad periods in the past, but now it's gone.」と言えます。
また、別の言い方で「In the past there had been a spell of dreadful times, but that seems to be long gone.」と言えます。
ご参考になれば幸いです。
アメリカ合衆国 
