Global max pooling is equal ordinary max pooling layer with pool size equals to the size of the input (minus filter size + 1, to be precise). You can see that MaxPooling1D takes a pool_length argument, whereas GlobalMaxPooling1D does not.
For example, if the input of the max pooling layer is 0,1,2,2,5,1,2, global max pooling outputs 5, whereas ordinary max pooling layer with pool size equals to 3 outputs 2,2,5,5,5 (assuming stride=1)
What is global max pooling layer and what is its advantage over maxpooling layer?