There are a few things to keep in mind when writing an acknowledgement for a history paper. First, you want to make sure to thank anyone who helped you with your research, whether it was providing advice, giving access to archives, or simply offering moral support. Second, you should try to keep your acknowledgements short and to the point; this is not the place to go into lengthy detail about everyone who helped you. Finally, you should express your gratitude in a sincere and professional manner.
With those guidelines in mind, here is a template you can use for writing an acknowledgement for a history paper:
I would like to thank [name] for their help with my research for this paper. [Their help] was essential to the completion of this work. I am also grateful to [name] for providing access to [relevant archives/documents/etc.].
Without their assistance, this paper would not have been possible. Thank you also to [name] for their constant support and encouragement throughout this process.
Thank you all for your help in making this paper a reality.